
827 S.W.2d 833 (1992)
Charles F. WALKER and Mary Jeanette Walker et al., Relators,
v.
The Honorable Anne PACKER, Judge, Respondent.
No. C-9403.
Supreme Court of Texas.
February 19, 1992.
Rehearing Overruled May 6, 1992.
Dissenting Opinion May 7, 1992.
*835 Les Weisbrod and Michael S. Box, Dallas, for relators.
Philipa Remington, Stephen W. Johnson, James A. Williams, Kevin J. Keith, Martha L. Strother, Gary W. Sibley, Dallas and Delmar L. Cain, Austin, for respondent.
Dissenting Opinion by Justice Gammage May 7, 1992.

OPINION
PHILLIPS, Chief Justice.
This original mandamus action involves two pre-trial discovery requests sought by *836 relators, plaintiffs in a medical malpractice lawsuit. The first discovery dispute involves documents which the plaintiffs seek from one of the defendants, while the second involves documents which they seek from a nonparty for impeachment purposes. As to the first matter, we hold that relators have not presented a sufficient record to demonstrate that the trial court clearly abused its discretion in failing to grant them all requested relief. As to the second, we hold that relators have an adequate remedy by appeal. Thus, mandamus is inappropriate, and we deny the writ.

The St. Paul and Aetna Records
Catherine Johanna Walker sustained brain damage at birth in January 1983. In January 1985, her parents, Charles F. and Mary Jeanette Walker, sued Dr. Paul Crider, the obstetrician, St. Paul Hospital, where Catherine was born, and Iris Jean White, a nurse attending at the delivery.
In August 1987, the Walkers served on St. Paul their third request for production of documents pursuant to Tex.R.Civ.P. 167. One request asked for:
Any and all writings, notes, documents, letters, etc., concerning, mentioning, alluding to, or making reference to (either directly or indirectly), the tape recorded statement given by Nurse White to an Aetna adjuster, including but not limited to any notes or entries in any Aetna adjuster's file, any attorney's file, or any file or writing in possession of any employee, representative or agent of St. Paul Hospital. This request is in reference to the tape recorded statement which you have been unable to locate, but which was previously requested....
St. Paul responded as follows:
In an effort to respond to this request, this Defendant again checked with all appropriate personnel and files at St. Paul Hospital and the law firm of Bailey and Williams. No such statement or taped recording was found. For the third time the Aetna Casualty and Surety Company was asked to check its records and files and a partially transcribed statement was located, a copy of which is attached. No taped recording was located.
Nearly two years later, the Walkers filed a motion to compel under Tex.R.Civ.P. 215, asserting that St. Paul failed to respond completely to the request.[1] The Walkers complained that "St. Paul Hospital did not even respond to what was requested in the request for productionthat is, writings, notes, and notations in the adjuster's file or attorney's file mentioning, alluding to, or making reference to the tape recorded statement of Nurse White." At about the same time, the Walkers also served on Aetna Casualty and Surety Company, St. Paul's insurer, an "Amended Notice of Intention to Take Deposition Upon Written QuestionsDuces Tecum," seeking, among other things, the same documents. Aetna moved to quash the notice.
The trial judge appointed a special master to review the Walkers' motion to compel and Aetna's motion to quash. After an evidentiary hearing on September 5, 1989, the master prepared findings, which formed the basis for two extensive orders signed by the trial court on September 20, 1989. In the first order, the court found that the Walkers were "entitled to all documentation sought in [the request] from the files of Defendant St. Paul or its attorney of record, but not from the files of Aetna Insurance Company, except as they may appear in the files of St. Paul or the attorneys of record of St. Paul." The court also stated that it "has been advised that St. Paul has supplied all documentation that is responsive to [the request], but that additional documentation will be made available *837 to the Court for in camera review." The court therefore sustained the Walkers' motion to compel "to the extent that on Friday, September 8, 1989 the Special Master will review in the Chambers of the 134th District Court the relevant portions of the St. Paul files and their attorney [sic] files, which may be in response to Plaintiff's request...." The court, however, did not order St. Paul to produce documents from Aetna's files for in camera inspection.[2]
After the master's September 8 in camera inspection, the court ordered discovery of three additional documents from the files of St. Paul and its attorneys, which it found "relate to the matters sought in discovery and should be supplied after irrelevant portions of such documents are stricken."
After unsuccessfully seeking relief in the court of appeals, the Walkers moved for leave to file a petition for writ of mandamus with this court, arguing that the trial court clearly abused its discretion by refusing to order St. Paul to produce the documents from Aetna's files and by ordering that portions of the other responsive documents be stricken. The Walkers contend that the order was a clear abuse of discretion because St. Paul 1) never objected to the Walkers' request for production, 2) had a superior right to the Walkers to compel production of the documents in Aetna's possession, and 3) never asked that any parts of the documents be excised.
The record before us does not include the statement of facts from the evidentiary hearing on the Walkers' motion to compel production. Without it, we cannot determine on what basis the trial judge and the special master reached their conclusions. Since we cannot assess whether or not the trial court's order was correct, we obviously cannot take the additional step of determining that the court's order, if incorrect, constituted a clear abuse of discretion.
As the parties seeking relief, the Walkers had the burden of providing this Court with a sufficient record to establish their right to mandamus relief. Since an evidentiary hearing was held, the Walkers had the burden of providing us not only a petition and affidavit, see Tex.R.App.P. 121(a)(2)(C) and (F), but also a statement of facts from the hearing. See, e.g., Cameron County v. Hinojosa, 760 S.W.2d 742, 744 (Tex.App.Corpus Christi 1988, orig. proceeding); Greenstein, Logan & Co. v. Burgess Mktg. Inc., 744 S.W.2d 170, 177 (Tex.App.Waco 1987, writ denied); see also Western Casualty & Surety Co. v. Spears, 730 S.W.2d 821, 822 (Tex.App. San Antonio 1987, orig. proceeding).[3] Having failed to meet this burden, the Walkers have not provided us with a record upon which they can establish their right to mandamus relief against St. Paul.

The Obstetrics Faculty Records
The second discovery dispute arises out of the Walkers' attempt to secure documentary evidence to impeach one of the defendants' expert witnesses, Dr. Larry Gilstrap, a faculty member in obstetrics at the University of Texas Health Science Center at Dallas ("the Center"). Gilstrap testified at his deposition that expert witness fees earned by obstetrics faculty members are deposited into a "fund" in the obstetrics "billing department"; that obstetrics faculty members get paid "indirectly" from this fund; that the fund is handled by Judy Wagers, a Center employee; and that he was unaware of any obstetrics department policy restricting faculty members from testifying for plaintiffs in medical malpractice cases.
*838 Thereafter, the Walkers noticed Wagers' deposition, requesting that she provide all documents regarding (1) the operation of the above-mentioned "fund" from 1985 to 1988; and (2) limitations placed upon obstetrics faculty members relating to their testimony in medical malpractice cases. The Center, on behalf of Wagers, moved to quash the notice, arguing that the request for documents was "vague and overly broad" and that production would be "costly and burdensome."
Two months later, in an unrelated lawsuit, the Walkers' counsel deposed Dr. Alvin L. Brekken, another obstetrics faculty member at the Center. Dr. Brekken testified that the obstetrics department's official policy, distributed in writing to all faculty members, requires a doctor to obtain authorization from other faculty members before testifying for any plaintiff in a medical malpractice case. Based on this testimony, the Walkers sought a court order to depose Wagers and obtain the requested documents.
After reviewing the Gilstrap and Brekken depositions and pleadings of counsel, the trial court ordered the Center to produce the documents for in camera review by the special master. Subsequently, in her September 20, 1989 order, the trial judge denied the discovery, stating in part:
[S]uch requested discovery is improper pursuant to the Rulings of the Supreme Court of Texas in Russell v. Young [452 S.W.2d 434 (Tex. 1970)], as the potential witness is not a party to the suit and the records do not relate to the subject matter of the suit, but are sought solely for the purpose of impeachment, according to the Plaintiffs' pleadings. Although noting that some of the documents "would be relevant to this cause of action," the court nevertheless denied discovery because "all such documents are controlled by the Russell decision."
In Russell, a party sought wholesale discovery of financial records of a potential medical expert witness who was not a party to the lawsuit.[4] The documents requested did not relate directly to the subject matter of the suit, but were sought solely in an attempt to impeach the potential witness by showing bias or prejudice. The credibility of the witness, however, had not yet been put in doubt. Under these circumstances, we held that the documents were not discoverable, and we directed the trial court to vacate its order allowing the requested discovery. 452 S.W.2d at 435. We reasoned that "[t]here is ... a limit beyond which pre-trial discovery should not be allowed." Id. at 437.
The present case is distinguishable. Here, the Walkers presented to the trial court evidence of a specific circumstance the Center's policy restricting the faculty's freedom to testify for plaintiffsraising the possibility that Dr. Gilstrap is biased. Thus, the Walkers are not engaged in global discovery of the type disapproved in Russell; rather, they narrowly seek information regarding the potential bias suggested by the witness' own deposition testimony and that of his professional colleague.
Our rules of civil procedure, and the federal rules upon which they are based, mandate a flexible approach to discovery. A party may seek any information which "appears reasonably calculated to lead to the *839 discovery of admissible evidence." Tex. R.Civ.P. 166b(2)(a). Evidence of bias of a witness is relevant and admissible. See Tex.R.Civ.Evid. 613(b).[5]
The trial court erred in failing to apply the foregoing rules to determine whether the documents were discoverable. Instead, the trial court simply read Russell as an absolute bar to discovery, even though the circumstances here are quite distinguishable. In so doing, the trial court misapplied the Russell holding. We expressly disapprove such a mechanical approach to discovery rulings.[6]
Having concluded that the trial court erred in denying the discovery based solely on Russell, we now must determine whether the appropriate remedy lies by writ of mandamus. "Mandamus issues only to correct a clear abuse of discretion or the violation of a duty imposed by law when there is no other adequate remedy by law." Johnson v. Fourth Court of Appeals, 700 S.W.2d 916, 917 (Tex.1985).[7] We therefore examine whether the trial court's error in the present case constituted a clear abuse of discretion and, if so, whether there is an adequate remedy by appeal.
1. Clear Abuse of Discretion
Traditionally, the writ of mandamus issued only to compel the performance of a ministerial act or duty. See Wortham v. Walker, 133 Tex. 255, 277, 128 S.W.2d 1138, 1150 (1939); Arberry v. Beavers, 6 Tex. 457 (1851); Helen A. Cassidy, The Instant Freeze-Dried Guide to Mandamus Procedure in Texas Courts, 31 S.Tex. L.Rev. 509, 510 (1990); Comment, The Expanding Use of Mandamus to Review Texas District Court Discovery Orders: An Immediate Appeal Is Available, 32 Sw. L.J. 1283, 1288 (1979).
Since the 1950's, however, this Court has used the writ to correct a "clear abuse of discretion" committed by the trial court. See, e.g., Joachim v. Chambers, 815 S.W.2d 234, 237 (Tex. 1991); Jampole v. Touchy, 673 S.W.2d 569, 574 (Tex. 1984); West v. Solito, 563 S.W.2d 240, 244 (Tex. 1978); Womack v. Berry, 156 Tex. 44, 50, 291 S.W.2d 677, 682 (1956). See generally, David W. Holman & Byron C. Keeling, Entering the Thicket? Mandamus Review of Texas District Court Witness Disclosure Orders, 23 St. Mary's L.J. 365, 390 (1991); Cassidy, 31 S.Tex.L.Rev. at 510; Note, The Use of Mandamus to Review Discovery Orders in Texas: An Extraordinary Remedy, 1 Rev.Litig. 325, 326-27 (1981); Comment, 32 Sw.LJ. at 1290.
A trial court clearly abuses its discretion if "it reaches a decision so arbitrary and unreasonable as to amount to a clear and prejudicial error of law." Johnson v. Fourth Court of Appeals, 700 S.W.2d at 917. This standard, however, has different applications in different circumstances.
With respect to resolution of factual issues or matters committed to the trial court's discretion, for example, the reviewing court may not substitute its judgment for that of the trial court. See Flores v. Fourth Court of Appeals, 111 S.W.2d 38, 41-42 (Tex.1989) (holding that determination *840 of discoverability under Tex.R.Civ.P. 166b(3)(d) was within discretion of trial court); Johnson, 700 S.W.2d at 918 (holding that trial court was within discretion in granting a new trial "in the interest of justice and fairness"). The relator must establish that the trial court could reasonably have reached only one decision. Id. at 917. Even if the reviewing court would have decided the issue differently, it cannot disturb the trial court's decision unless it is shown to be arbitrary and unreasonable. Johnson, 700 S.W.2d at 918.
On the other hand, review of a trial court's determination of the legal principles controlling its ruling is much less deferential. A trial court has no "discretion" in determining what the law is or applying the law to the facts. Thus, a clear failure by the trial court to analyze or apply the law correctly will constitute an abuse of discretion, and may result in appellate reversal by extraordinary writ. See Joachim v. Chambers, 815 S.W.2d 234, 240 (Tex. 1991) (trial court abused discretion by misinterpreting Code of Judicial Conduct); NCNB Texas National Bank v. Coker, 765 S.W.2d 398, 400 (Tex.1989) (trial court abused discretion by failing to apply proper legal standard to motion to disqualify counsel); Eanes ISD v. Logue, 712 S.W.2d 741, 742 (Tex.1986) (trial court abused discretion by erroneously finding constitutional violation).
In determining whether the trial court abused its discretion in the present case, we treat the trial court's erroneous denial of the requested discovery on the sole basis of Russell as a legal conclusion to be reviewed with limited deference to the trial court. This is consistent with our approach in previous mandamus proceedings arising out of the trial court's interpretation of legal rules. Cf. Axelson, Inc. v. Mcllhany, 798 S.W.2d 550, 555 (Tex. 1990); Barnes v. Whittigton, 751 S.W.2d 493, 495-96 (Tex.1988); Terry v. Lawrence, 700 S.W.2d 912, 913-14 (Tex. 1985). Under this analysis, the trial court's erroneous interpretation of the law constitutes a clear abuse of discretion.
2. Adequate Remedy by Appeal
In order to determine whether the writ should issue, however, we must further decide whether the Walkers have an adequate remedy by appeal.
Mandamus will not issue where there is "a clear and adequate remedy at law, such as a normal appeal." State v. Walker, 679 S.W.2d 484, 485 (Tex.1984). Mandamus is intended to be an extraordinary remedy, available only in limited circumstances. The writ will issue "only in situations involving manifest and urgent necessity and not for grievances that may be addressed by other remedies." Holloway v. Fifth Court of Appeals, 767 S.W.2d 680, 684 (Tex.1989) (quoting James Sales, Original Jurisdiction of the Supreme Court and the Courts of Civil Appeals of Texas in Appellate Procedure in Texas, § 1.4[l][b] at 47 (2d ed. 1979)). The requirement that persons seeking mandamus relief establish the lack of an adequate appellate remedy is a "fundamental tenet" of mandamus practice. Holloway, 767 S.W.2d at 684.
Our requirement that mandamus will not issue where there is an adequate remedy by appeal is well-settled.[8] On a few occasions, however, we have not focused *841 on this requirement when applying mandamus review of discovery orders. For example, in Barker v. Dunham, 551 S.W.2d 41 (Tex.1977), the trial court refused to compel defendant's representative to answer certain deposition questions, and the plaintiff applied to this Court for a writ of mandamus. We concluded that the trial court had abused its discretion, and ordered that the writ conditionally issue. We never discussed the well-settled requirement of inadequate remedy by appeal.
A few months later, in Allen v. Humphreys, 559 S.W.2d 798 (Tex.1977), the Court again conditionally issued a writ of mandamus to correct a discovery abuse without considering whether the relator had an adequate remedy by appeal. The real party in interest in Allen raised this argument, but the Court avoided the issue by citing Barker. Id. at 801.
Commentators quickly criticized the Barker and Allen opinions. See James Sales, Pre-Trial Discovery in Texas, 31 Sw.LJ. 1017, 1033 (1977); Comment, The Expanding Use of Mandamus to Review Texas District Court Discovery Orders: An Immediate Appeal Is Available, 32 Sw.LJ. 1283, 1300 (1979) (In most cases "forcing a party to await the completion of the trial in order to seek appellate review will not endanger his substantial rights...."); Note, Mandamus May Issue To Compel A District Judge to Order Discovery, 9 Tex.Tech L.Rev. 782 (1978) (mandamus should not be a substitute for appeal).
In Jampole v. Touchy, 673 S.W.2d 569 (Tex.1984), the Court again used the extraordinary writ of mandamus to compel discovery which had been denied by the trial court. Unlike in Barker and Allen, however, the Court in Jampole addressed whether relator had an adequate appellate remedy. The underlying suit in Jampole was a products liability action, and the disputed discovery materials included alternate design and assembly documents. The Court held that relator did not have an adequate remedy by appeal because denial of this discovery effectively prevented relator from proving the material allegations of his lawsuit. 673 S.W.2d at 576. Remedy by appeal in a discovery mandamus is not adequate where a party is required "to try his lawsuit, debilitated by the denial of proper discovery, only to have that lawsuit rendered a certain nullity on appeal...."
Id.
Although the Court in Jampole recognized the need to address whether relator had an adequate remedy by appeal, it expressly refused to overrule Barker and Allen. Id. Perhaps because of this, we have on several occasions since Jampole used mandamus to correct discovery errors without considering whether the relator had an adequate appellate remedy. See Loftin v. Martin, 776 S.W.2d 145 (Tex. 1989); Barnes v. Whittington, 751 S.W.2d 493 (Tex.1988); Lunsford v. Morris, 746 S.W.2d 471 (Tex.1988); Turbodyne Corp. v. Heard, 720 S.W.2d 802 (Tex.1986); Terry v. Lawrence, 700 S.W.2d 912 (Tex. 1985); Lindsay v. O'Neill, 689 S.W.2d 400 (Tex. 1985).
On many other occasions, however, we have still required a showing of inadequate *842 remedy by appeal in mandamus proceedings involving other types of pre-trial orders, even those involving discovery. See, e.g., TransAmerican Natural Gas Corp. v. Powell, 811 S.W.2d 913, 919 (Tex.1991); Hooks v. Fourth Court of Appeals, 808 S.W.2d 56, 59-60 (Tex.1991); Bell Helicopter Textron, Inc., v. Walker, 787 S.W.2d 954, 955 (Tex.1990); Stringer v. Eleventh Court of Appeals, 720 S.W.2d 801, 801-02 (Tex. 1986). In Hooks, for example, we reaffirmed that the "cost or delay of having to go through trial and the appellate process does not make the remedy at law inadequate." 808 S.W.2d at 60.
The requirement that mandamus issue only where there is no adequate remedy by appeal is sound, and we reaffirm it today. No mandamus case has ever expressly rejected this requirement, or offered any explanation as to why mandamus review of discovery orders should be exempt from this "fundamental tenet" of mandamus practice. Without this limitation, appellate courts would "embroil themselves unnecessarily in incidental pre-trial rulings of the trial courts" and mandamus "would soon cease to be an extraordinary writ." Braden v. Downey, 811 S.W.2d 922, 928 (Tex.1991). We thus hold that a party seeking review of a discovery order by mandamus must demonstrate that the remedy offered by an ordinary appeal is inadequate. We disapprove of Barker, Allen, and any other authorities to the extent they might be read as abolishing or relaxing this rule.
We further hold that an appellate remedy is not inadequate merely because it may involve more expense or delay than obtaining an extraordinary writ. As we observed in Iley v. Hughes, the "delay in getting questions decided through the appellate process ... will not justify intervention by appellate courts through the extraordinary writ of mandamus. Interference is justified only when parties stand to lose their substantial rights." 158 Tex. at 368, 311 S.W.2d at 652.
On some occasions, this Court has used, or at least mentioned, the more lenient standard first articulated in Cleveland v. Ward, 116 Tex. 1, 14, 285 S.W. 1063, 1068 (Tex.1926), that the remedy by appeal must be "equally convenient, beneficial, and effective as mandamus." See, e.g., Jampole v. Touchy, 673 S.W.2d 569, 576 (Tex.1984); Crane v. Tunks, 160 Tex. 182, 190, 328 S.W.2d 434, 439 (Tex.1959). This standard, literally applied, would justify mandamus review whenever an appeal would arguably involve more cost or delay than mandamus. This is unworkable, both for individual cases and for the system as a whole. Mandamus disrupts the trial proceedings, forcing the parties to address in an appellate court issues that otherwise might have been resolved as discovery progressed and the evidence was developed at trial. Moreover, the delays and expense of mandamus proceedings may be substantial. This proceeding, for example, involving rulings on collateral discovery matters, has delayed the trial on the merits for over two years. The impact on the appellate courts must also be considered. We stated in Braden that "[t]he judicial system cannot afford immediate review of every discovery sanction." 811 S.W.2d 922, 928. It follows that the system cannot afford immediate review of every discovery order in general.[9] We therefore disapprove of Cleveland, Crane, Jampole and any other authorities to the extent that they imply that a remedy by appeal is inadequate merely because it might involve more delay or cost than mandamus.
Justice Doggett's dissent argues that because discovery errors often constitute harmless errors under Tex.R.App.P. 81(b)(1), parties denied mandamus relief will be deprived of any remedy since the *843 error will not provide a basis for appellate reversal. This is nothing more than a thinly disguised attack on the harmless error rule. Avoiding interlocutory appellate review of errors that, in the final analysis, will prove to be harmless, is one of the principal reasons that mandamus should be restricted.
Justice Doggett's dissent also suggests that we will be unable to develop a coherent body of discovery law without unrestricted mandamus review. We do not think, however, that losing parties will be reluctant to raise perceived discovery errors on appeal, nor will an appellate court be foreclosed from writing on discovery issues, even when the error may be harmless. See, e.g., Lovelace v. Sabine Consolidated, Inc., 733 S.W.2d 648, 652-53 (Tex. AppHouston [14th Dist] 1987, writ denied).
Nor are we impressed with the dissenters' claim that strict adherence to traditional mandamus standards will signal an end to effective interlocutory review for some parties or classes of litigants. There are many situations where a party will not have an adequate appellate remedy from a clearly erroneous ruling, and appellate courts will continue to issue the extraordinary writ. In the discovery context alone, at least three come to mind.
First, a party will not have an adequate remedy by appeal when the appellate court would not be able to cure the trial court's discovery error. This occurs when the trial court erroneously orders the disclosure of privileged information which will materially affect the rights of the aggrieved party, such as documents covered by the attorney-client privilege, West v. Solito, 563 S.W.2d 240 (Tex. 1978), or trade secrets without adequate protections to maintain the confidentiality of the information. Automatic Drilling Machines v. Miller, 515 S.W.2d 256 (Tex. 1974). As we noted in Crane: "After the [privileged documents] had been inspected, examined and reproduced... a holding that the court had erroneously issued the order would be of small comfort to relators in protecting their papers." 160 Tex. at 190, 328 S.W.2d at 439. It may also occur where a discovery order compels the production of patently irrelevant or duplicative documents, such that it clearly constitutes harassment or imposes a burden on the producing party far out of proportion to any benefit that may obtain to the requesting party. See, e.g., Sears, Roebuck & Co. v. Ramirez, 824 S.W.2d 558, 35 Tex.Sup.Ct.J. 454 (1992) (demand for tax returns); General Motors Corp. v. Lawrence, 651 S.W.2d 732 (Tex. 1983) (demand for information about all vehicles for all years).
Second, an appeal will not be an adequate remedy where the party's ability to present a viable claim or defense at trial is vitiated or severely compromised by the trial court's discovery error. It is not enough to show merely the delay, inconvenience or expense of an appeal. Rather, the relator must establish the effective denial of a reasonable opportunity to develop the merits of his or her case, so that the trial would be a waste of judicial resources. We recently held that when a trial court imposes discovery sanctions which have the effect of precluding a decision on the merits of a party's claimssuch as by striking pleadings, dismissing an action, or rendering default judgmenta party's remedy by eventual appeal is inadequate, unless the sanctions are imposed simultaneously with the rendition of a final, appealable judgment. TransAmerican Natural Gas Corp. v. Powell, 811 S.W.2d 913, 919 (Tex. 1991). Similarly, a denial of discovery going to the heart of a party's case may render the appellate remedy inadequate.
Finally, the remedy by appeal may be inadequate where the trial court disallows discovery and the missing discovery cannot be made part of the appellate record, or the trial court after proper request refuses to make it part of the record, and the reviewing court is unable to evaluate the effect of the trial court's error *844 on the record before it. See Tom L. Scott, Inc. v. Mcllhany, 798 S.W.2d 556, 558 (Tex. 1990) ("[M]andamus is the only remedy because the protective order shields the witnesses from deposition and thereby prevents the evidence from being part of the record."); see generally Jampole, 673 S.W.2d at 576 ("Because the evidence exempted from discovery would not appear in the record, the appellate courts would find it impossible to determine whether denying the discovery was harmful."). If the procedures of Tex.R.Civ.P. 166b(4) are followed, this situation should only rarely arise. If and when it does, however, the court must carefully consider all relevant circumstances, such as the claims and defenses asserted, the type of discovery sought, what it is intended to prove, and the presence or lack of other discovery, to determine whether mandamus is appropriate.[10]
In the present case, the Walkers seek documents from the Center to impeach one defendant's expert witness. This information is not privileged, burdensome or harassing, nor does it vitiate or severely compromise the Walkers' ability to present a viable claim. In fact, as we have already noted, the trial court may ultimately conclude that it is not admissible or even discoverable. Finally, although the materials are not before us, they were considered below, and we know of no reason why they would not be available on appeal. Therefore, under our traditional standards of mandamus review, as measured by the factors we mention above, the Walkers have an adequate remedy by appeal and mandamus is inappropriate.
For the above reasons, we conclude that the Walkers have not established their right to relief by mandamus on either discovery matter. Therefore, we deny the Walkers' petition for writ of mandamus.
GONZALEZ, J., concurs and files an opinion.
DOGGETT, J., dissents and files an opinion, joined by MAUZY, J.
GAMMAGE, J., dissents and files an opinion.
GONZALEZ, Justice, concurring.
I agree with the court's disposition of this cause but disagree with the court's opinion regarding the "Obstetrics Faculty Records." Specifically, I disagree with the court's attempt to distinguish Russell v. Young, 452 S.W.2d 434 (Tex. 1970). Nevertheless, I concur in the result.
Russell holds that wholesale discovery of the private records of a non-party witness is not permitted if the sole purpose for discovery is to impeach the credibility of the non-party.[1] 452 S.W.2d at 435. The policy considerations of Russell still apply today. By disapproving of Russell as "a mechanical approach to discovery rulings," at 839, the court forces trial courts to get further involved in discovery matters. This increases the backlog, delay, and cost of litigation by creating the need for more hearings.
In the instant case, the plaintiffs sought to discover documents from the University of Texas Health Science Center to confirm the existence of a written policy restricting faculty members from testifying for plaintiffs in medical malpractice cases. This policy was sought for use in impeaching defendant's expert witness, Dr. Gilstrap. In refusing discovery, the trial court concluded *845 that the relevance of this material was limited to impeachment. As such, the requested documents fell squarely within the prohibition of Russell.
Despite the court's mischaracterization of Russell, the issues and type of evidence sought here and in Russell are identical. Just as in Russell, the records sought in the instant case did not relate directly to the subject matter of the suit. The only difference between the present case and Russell is the identity of the party seeking the information. In Russell, a defendant sought evidence to impeach the plaintiffs' expert; here, the plaintiff sought evidence to impeach a defendant's expert. Surely, we cannot have a rule that changes in application depending on whether the relator is a plaintiff or a defendant in the trial court.
In my opinion, the court strains to distinguish Russell. The court suggests that the trial judge made a mistake in her ruling by failing to read Russell in conjunction with the rules of civil procedure and evidence. However, when we adopted the new Texas Rules of Civil Evidence, there was no discussion whatsoever that, by their adoption, we intended to reject the settled rule that information sought solely for impeachment of a non-party is not discoverable. Russell, 452 S.W.2d at 435; see also W.W. Rodgers & Sons Produce Co. v. Johnson, 673 S.W.2d 291, 294-95 (Tex. App.Dallas 1984, orig. proceeding). Furthermore, the scope of discovery has not changed in the twenty years since Russell has been on the books. When Russell was decided, the scope of discovery was codified in Texas Rule of Civil Procedure 186a. It provided in pertinent part that:
[p]arties may obtain discovery regarding any matter which is relevant to the subject matter in the pending action whether it relates to the claim or defense of the party seeking discovery or the claim or defense of any other party.
This same text is now codified in Rule 166b(2)(a). Clearly, impeachment evidence regarding collateral matters would not relate to the subject matter of the pending action.
Implicitly, the court concludes that the credibility of a non-party witness alone is a relevant avenue of inquiry and, thus, is a matter properly open to discovery under some new, broader definition of relevancy.
While I agree that the definition of relevance in Rule 401 of the Texas Rules of Civil Evidence includes matters bearing on credibility, this alone does not explain or distinguish Russell. A witness' credibility has always been a relevant matter. As the United States Supreme Court has said: "[p]roof of bias is almost always relevant because the jury, as finder of fact and weigher of credibility, has historically been entitled to assess all evidence which might bear on the accuracy and truth of a witness' testimony." United States v. Abel, 469 U.S. 45, 52, 105 S.Ct. 465, 469, 83 L.Ed.2d 450 (1984). Yet in Russell, we said that a trial court lacked "authority" to order discovery from a non-party solely for purposes of impeachment. 452 S.W.2d at 435. We chose to withdraw all discretion in this particular area of discovery. Russell concedes that impeachment evidence may be relevant and admissible at trial, but holds that it cannot be discovered from a non-party for its own sake prior to trial. 452 S.W.2d at 436.
The fact that a matter may have some relevance yet not be subject to discovery is hardly a novel concept. The basic premise of the rules of discovery is to weigh the legitimate needs of litigation against the other rights and values that would be irreparably harmed by unfettered discovery. Russell strikes the proper balance by protecting non-party witnesses from indiscriminate invasions into their private lives where the information sought would not appreciably shed light on the issues of the case.
Furthermore, the decision in Russell was not grounded on whether the credibility of the witness had been placed in doubt. Instead, the court highlighted the fact that *846 the witness had not offered testimony at trial nor was his deposition introduced into evidence at trial. The court said:
Relator has not yet taken the witness stand nor has his deposition been introduced into evidence because there has not yet been a trial; relator's records cannot possibly have impeachment value because there is nothing yet to impeach and there may never be anything to impeach, depending upon the contents of the testimony, if any, which is introduced during the trial of the lawsuit.
Russell, 452 S.W.2d at 437. Thus, it is evident that the court has today reinterpreted Russell with little or nothing to gain in a way that further obscures the proper scope of discovery.
I am concerned that as a result of today's ruling, some non-parties will be subjected to harassment and intrusion into their private lives, and that trial courts will be inundated with hearings on collateral issues far afield from the merits of the cause of action or defense. The court has attempted to fix something that was not broken. This reinterpretation of Russell will further tax our overburdened judicial system without appreciably benefiting the litigants or the system.
Finally, for the reasons expressed in Joachim v. Chambers, 815 S.W.2d 234, 241 (Tex.1991) (Gonzalez, J., dissenting), I agree with the clarification of the standards for the issuance of mandamus.
DOGGETT, Justice, dissenting.
Them that's got shall get

Them that's not shall lose.
God Bless The Child[1]
With a double standard, the majority strikes a devastating blow at the most direct method of curbing abuses of judicial power. Many judicial excesses far beyond the scope of anything alleged in this particular case will henceforth receive only an official nod and wink from the Texas Supreme Court.
Mandamus is the legal tool by which appellate courts can promptly correct arbitrary and capricious rulings by trial judges. Today's opinion announces that this remedy will be available to support concealment of the truth but not its disclosure. Mandamus is officially declared a one-way street in the Texas courtsour judiciary can help to hide but not to detect.
Despite a determination that a "clear abuse of discretion" has occurred in this particular case, at 840, all relief is denied. Finding a wrong and denying a remedy echoes the logic of the majority's recent conclusion that a tax is unconstitutional but must be paid anyway. See Carrollton-Farmers Branch Indep. Sch. Dist. v. Edgewood Indep. Sch. Dist, 826 S.W.2d 489, 524 (1992) (Edgewood III) (Doggett, J., dissenting). Rather than correcting the abuse, the court simply gives the Walkers the same message it gave Texas taxpayerswait. Only after a full jury trial based upon incomplete discovery will the judiciary even consider any possibility of relief.
For those who have previously sought more specific guidelines for the use of mandamus concerning discovery orders, the majority responds with not one but two standards for reviewing trial court action: orders compelling discovery may be immediately corrected; review of denied discovery is postponed indefinitely in a manner to ensure that no meaningful relief will ever be forthcoming.

I.
What a different path this court now pursues than that so recently proclaimed in its unanimous decision that
Discovery is ... the linchpin of the search for truth, as it makes "a trial less *847 a game of blind man's bluff and more a fair contest with the issues and facts disclosed to the fullest practicable extent."
State v. Lowry, 802 S.W.2d 669, 671 (Tex. 1991) (quoting United States v. Proctor & Gamble Co., 356 U.S. 677, 682, 78 S.Ct. 983, 986, 2 L.Ed.2d 1077 (1958)). Similarly ignored are our recent, unanimous writings in Axelson, Inc. v. Mcllhany, 798 S.W.2d 550, 553, 555 (Tex.1990, orig. proceeding) ("[Discovery should provide] the fullest knowledge of the facts and issues prior to trial.... [T]he ultimate purpose of discovery... is to seek the truth...."); and Tom L. Scott, Inc. v. Mcllhany, 798 S.W.2d 556, 559 (Tex.1990, orig. proceeding) ("The primary policy behind discovery is to seek truth so that disputes may be decided by facts that are revealed rather than concealed."). Without mandamus review to add meaning to these laudatory expressions, they are just hollow words. The new signal is clearcircumvent discovery and conceal information.
Today's opinion reflects the radical change in philosophy which has taken firm hold in this courtdiscovery is no longer a search for truth, it is merely a game of hide and seek. No longer may appellate courts intercede through mandamus even for the trial court's complete abuse of discretion in denying access to vital data; under the newly-announced double standard, intervention can, however, be accorded for those who persevere in evasion.
When a local business is defrauded, when a community is exposed to dangerous toxic wastes, when a manufacturer ignores reports that a safety design change would reduce user injuries, when a monopoly extorts unfair gain from the public, when discrimination results in job loss, and in numerous other circumstances, the burden of proving wrongdoing is exceedingly difficult to satisfy without obtaining evidence of that wrong from the files of the perpetrator. In such situations denial of discovery effectively means denial of all relief. That reality does not go unrecognized by today's majority.
Entities that begin litigation in control of most of the relevant evidence can often defeat their adversaries simply by denying them the power of information:
[T]hose with established positions of power are more likely to ... win by preventing their adversaries from producing evidence; they are less likely to be in the position of having to extract evidence from their opponents to make out their case.
23 Charles A. Wright & Kenneth W. Graham, Jr., Federal Practice & Procedure § 5422, at 674 (1980). With its separate and unequal treatment of litigants, the majority gives yet another edge to the already advantaged. Providing immediate review for orders that start the flow of information but refusing to consider those that stop it, the majority once again expresses its preference for helping the powerful over the seemingly powerless. Those opposing meaningful discovery
tend to be institutions rather than individuals, and tend to be among the more wealthy and powerful segments of society. A review system that gives priority (that is, immediate review) to the complaints of privilege holders, but which consigns the complaints of parties seeking discovery until after final judgment, gives an advantage to those wealthy institutional litigants. They have the power to achieve more favorable results during the pretrial process; their opponents must wait.
Elizabeth G. Thornburg, Interlocutory Review of Discovery Orders: An Idea Whose Time Has Come, 44 Sw.LJ. 1045, 1082 (1990) (hereinafter Review of Discovery Orders ) (footnote omitted).[2] In this way the *848 majority ensures that the scales of justicewhich at the onset of litigation are often in reality unevennever achieve balance.
Until this court included discovery orders within the scope of mandamus review, very few reported opinions addressed this important subject. Trial judges were effectively accorded unlimited discretion with a "resulting atmosphere [that] was very hostile to discovery." Id. at 1071. As a practical matter, discovery battles, often both complex and time-consuming, were shunned. When the party controlling vital data exercises the power of withholding it, fighting every important request, the judicial command "go work it out" often amounts to a denial of meaningful discovery. The mudwrestling that frequently ensues in such contests may discourage a trial judge from determining who is acting fairly and who started the fight. If mandamus is not available to correct ill-considered or hasty denials, the hope for ultimate justice in complex litigation is prematurely crushed. The majority's decision today marks a return to those dark ages when discovery was regularly denied as the path of least resistance and greatest convenience for the judiciary.

II.
By its very nature, discovery involves a search for what is largely unknown from someone who may have an incentive to make that search as long and tortuous as possible. Efforts to prevent discovery have been limited only by the boundless imagination of the top legal talent in America. Requests are either too broad or too narrow; records produced are either minimal or in such voluminous, disorganized form as to make locating relevant information most difficult; vital documents vanish in "routine document destruction" programs or are misplaced. Accordingly, our discovery rules have required continual revision to cope with the newest ways invented by those intent on subverting the process. Each revision of the Texas Rules of Civil Procedure during the last decade has included attempted clarification and improvement of discovery procedures. This has produced a body of law that is "complex and rapidly evolving." David W. Holman & Byron C. Keeling, Entering the Thicket? Mandamus Review of Texas District Court Witness Disclosure Orders, 23 St. Mary's L.J. 365, 375 (1991) (hereinafter Mandamus of Disclosure Orders).
Given the creativity of those who would thwart discovery, rules of procedure cannot be drawn to provide clear guidance in every situation; judicial interpretation is essential. The more complicated the rule, the more necessary the construction and the greater the likelihood for misinterpretation. See id. at 386 ("Erroneous interpretations of these changes ... are likely with the absence of prior significant precedent.... [and] could have a substantial effect on the subsequent course of a lawsuit."). This court's responsibility does not and cannot end when the text of promulgated amendments appears in the Texas Bar Journal. Rather, the court has a duty both to make the rules and to interpret them.
Our American system of jurisprudence is founded on the precept that it is of great benefit to have a written body of case law construing controlling legal principles and applying them to particular facts. This approach is undeniably desirable in the discovery context:
In a system where trial court decisions are unreported and have no precedential value, the creation of a body of reported appellate case law regarding discovery has substantial value. Case law on discovery promotes uniform interpretation of the discovery rules and, in time, decreases the opportunity for individual *849 judge's biases to shape discovery outcomes. Reported decisions develop clear rules, where rules are possible, and narrow the range of judicial discretion in other areas simply by providing numerous cases finding that the trial court did or did not abuse its discretion. Such case law can be particularly helpful in a jurisdiction that has recently amended its discovery rules. Over time, the existence of discovery case law may even clarify the rules sufficiently so as to decrease the number of disputes in the trial court.
Review of Discovery Orders at 1080 (footnotes omitted). Appellate opinions properly applying mandamus produce, then, both more consistency and more accuracy in trial court decisions. See id. at 1077.[3]
The role of this court is particularly important in answering novel or significant questions of discovery law. See Mandamus of Disclosure Orders at 376 ("[Pretrial appellate review of [important discovery] questions could lend critical guidance to the development of Texas discovery practice."). Rather than avoiding its responsibility, this court should utilize mandamus review to reduce the abuse of judicial power when "a unique question of discovery" law is presented. David West, Note, The Use of Mandamus to Review Discovery Orders in Texas: An Extraordinary Remedy, 1 Rev.Litigation 325, 327 (1981) (hereinafter The Use of Mandamus).
Most trial court mistakes denying discovery result from the need to make repeated, quick decisions based upon limited information. Recognizing this circumstance, trial judges sometimes actually encourage litigants to raise disputed rulings affecting truly vital matters for appellate examination through mandamus by automatically staying their orders. Refusal of prompt appellate review not only denies a party its rights but may also deprive a trial court of desired guidance.
Today's opinion appropriately recognizes that "this Court will not grant mandamus relief unless we determine that the error is of such importance to the jurisprudence of the state as to require correction." At 839 n. 7. But under the standard announced, questions of importance concerning judicially-approved concealment of facts will never be considered. The significance to the state's jurisprudence of a ruling should certainly not be controlled by whether the order granted or denied discovery.

III.
With mandamus now severely limited, many important issues will not be reviewed. See generally Review of Discovery Orders at 1056; The Use of Mandamus at 337 & n. 94. Abuses of judicial power will go forever uncorrected when the party disallowed discovery, realizing the difficulty of proving a case with less than full information and the uphill task of maintaining a successful appeal, is either forced to settle or forgoes a costly and extended appeal following defeat on the entire case. Nor will improper rulings ever be reviewed where one denied discovery, although severely handicapped, nonetheless prevails at trial.
Where appeals do occur, remedies will be rare even for egregious pretrial rulings. To succeed in this endeavor, one must show that
the error complained of amounted to such a denial of the rights of appellant as *850 was reasonably calculated to cause and probably did cause rendition of an improper judgment in the case, or was such as probably prevented the appellant from making a proper presentation of the case to the appellate court.
Tex.R.App.P. 81(b). This standard is universally regarded as a "more difficult hurdle" than abuse of discretion. Helen A. Cassidy, The Instant Freeze-Dried Guide to Mandamus Procedure in Texas Courts, 31 S.Tex.L.Rev. 509, 512 (1990). As another commentator has aptly concluded,
only an unusual discovery order would be dispositive enough to show the harmful error that most jurisdictions require for appellate reversal. Many appellants, therefore, would not even raise the discovery points on appeal.
Review of Discovery Orders at 1056; see also Mandamus of Disclosure Orders at 376 n. 40 (observing that, because of the harmless error rule, many discovery rulings are not pursued on appeal). In denying mandamus today, the majority closes and locks the appellate courthouse door to any meaningful consideration of numerous significant matters.

IV.
Only with the tragic recent change in course by this court's majority has such denial of access become acceptable. Previously both this court and the courts of appeals had employed their writ power as necessary to correct the abusive refusal of discovery. Among those cases providing the foundation for appropriate mandamus review is Barker v. Dunham, 551 S.W.2d 41 (Tex.1977, orig. proceeding), in which the trial court had overruled a motion to complete an expert witness's deposition and to compel production of his work papers. We interceded, stating that: "It is settled that the writ of mandamus may issue in a discovery proceeding to correct a clear abuse of discretion by a trial judge." Id. at 42. Similarly, in Allen v. Humphreys, 559 S.W.2d 798 (Tex.1977, orig. proceeding), the trial court refused to order discovery of tests, surveys and complaints by similarly affected persons. This court found an abuse of discretion and granted the writ, despite the argument that the plaintiff had "an adequate remedy via the normal appellate process." Id. at 801. It is difficult to perceive, in light of this argument and the court's subsequent grant of mandamus relief, how the majority can now claim that "we [had] not focused" on the requirement of an inadequate remedy by appeal in Allen and on, admittedly, a "few [other] occasions." At 840-841.
Following these two opinions, this court has not hesitated to consider and correct the wrongful denial of discovery. By issuing mandamus to rectify an erroneous trial court ruling refusing discovery in Jampole v. Touchy, 673 S.W.2d 569 (Tex.1984, orig. proceeding), this court recognized that appeal is not an adequate remedy:
[Requiring a party to try his lawsuit, debilitated by the denial of proper discovery, only to have that lawsuit rendered a certain nullity on appeal, falls well short of a remedy by appeal that is "equally convenient, beneficial, and effective as mandamus."
Id. at 576 (quoting Crane v. Tunks, 160 Tex. 182, 190, 328 S.W.2d 434, 439 (1959) (citation omitted)); see also Cleveland v. Ward, 116 Tex. 1, 14, 285 S.W. 1063, 1068 (Tex.1926).
A trial court's unwillingness to order the production of accident scene photographs was overturned by mandamus in Terry v. Lawrence, 700 S.W.2d 912 (Tex.1985, orig. proceeding). In Lindsey v. O'Neill, 689 S.W.2d 400, 402 (Tex.1985, orig. proceeding) (per curiam), the court overturned by mandamus an order limiting the scope of a deposition and quashing the accompanying document request. A blanket order protecting hospital records was similarly vacated by mandamus in Barnes v. Whittington, 751 S.W.2d 493 (Tex.1988, orig. proceeding). In Lunsford v. Morris, 746 S.W.2d 471 (Tex.1988, orig. proceeding), this court again granted mandamus to remedy a trial court's erroneous disallowance *851 of relevant discovery. See also Loftin v. Martin, 776 S.W.2d 145 (Tex.1989, orig. proceeding) (correcting by mandamus wrongful denial of discovery); Turbodyne Corp. v. Heard, 720 S.W.2d 802 (Tex.1986, orig. proceeding) (per curiam) (mandamus directing trial court to rescind order denying discovery of documents from insurer in subrogation action); Ginsberg v. Fifth Court of Appeals, 686 S.W.2d 105 (Tex. 1985, orig. proceeding) (erroneous bar of deposition by court of appeals cured by mandamus).[4]
It is only after fifteen years of repeated judicial reliance upon Barker and Allen in the issuance of numerous opinions that we learn these precedents of our court are not good law. This is all the more strange in that we had explicitly refused to overrule them. When that very request was urged in Jampole, 673 S.W.2d at 576, our answer was unmistakable: "We decline to do so." But the majority's new answer is simple: "Line them up against the wall." What does it matter that a dozen or more Texas Supreme Court cases and countless decisions of the courts of appeals are to the contrary? They can be disposed of in a mass execution of precedent.[5] Today's firing squad announces that it is only answering the command of Jim Sales and two law students who separately criticized the court during the period 1977-79. At 840-841. It thereby rationalizes constructing so distorted a standard on the corpses of so many prior authorities.
One of the most significant casualties is Jampole v. Touchy, which has formed the centerpiece for discovery in litigation over defective products and toxic substances for almost a decade. The majority, in a massive understatement, "disapproves" Jampole "to the extent [it implies] that a remedy by appeal is inadequate merely because it might involve more delay or cost than mandamus." At 842. Although leaving untouched for now this court's prior writing on the proper scope of discovery, the majority has in fact overruled that landmark precedent in its entirety. Despite a gross abuse of discretion in denying critical discovery in Jampole, the majority's only correction by mandamus would be to require inclusion of the disputed materials in *852 the record, to await a deferred and meaningless appellate review.

V.
Instead of affording the relief that prior rulings demand, the majority announces, after considerable mental gymnastics, that "at least three [discovery situations] come to mind" where mandamus is justified, at 843; then it strangely proceeds to describe six. The first three instances where remedy by appeal is inadequate stem from a trial court's wrongful allowance of discovery. First, mandamus will issue if "disclosure of privileged information ... will materially affect the rights of the aggrieved party." At 843. This requisite is easily fulfilled with discovery objections that include an assertion of privilege, the violation of which necessarily impinges on the objecting party's rights.
Second, mandamus will issue when a trial court orders the disclosure of "trade secrets without adequate protections to maintain the confidentiality of the information." At 843 (citing, without discussion, Automatic Drilling Macks., Inc. v. Miller, 515 S.W.2d 256 (Tex.1974, orig. proceeding)). Posing numerous problems, this hastily-drawn exception has no relevance to the instant case and was concocted by the majority without any briefing or argument by counsel. One privilege is thereby unjustifiably elevated above all others. Moreover, the writing implies an absolute protection of trade secrets from discovery when in fact this privilege is most definitely qualified, as recognized by Automatic Drilling, 515 S.W.2d at 259,[6] the rule itself, Tex.R.Civ.Evid. 507 (trade secrets not protected when nondisclosure conceals fraud or works injustice), and even Mr. Sales, whose writing purportedly warranted today's brash action.[7] Nor does this exception consider the availability in some cases of the interlocutory appeal mechanism provided in Tex.R.Civ.P. 76a(8) to address the adequacy of a protective order. See Eli Lilly & Co. v. Marshall, Order Granting Leave to File Petition for Writ of Mandamus (Doggett, J., dissenting), 829 S.W.2d 156 (Tex.1991).
The third situation requiring mandamus is an "order [that] compels the production of patently irrelevant or duplicative documents, such that it clearly constitutes harassment or imposes a burden on the producing party far out of proportion to any benefit that may obtain to the requesting party." At 843. This "catch-all" exception indeed makes the extraordinary writ of mandamus an ordinary one. In almost any complex litigation, the claim of burden is essentially a form objection to discovery. It is difficult to perceive a dispute in which the party seeking to obstruct the process could not and, after today's decision, will not claim harassment or imposition of an undue burden. See, e.g., Sears, Roebuck & Co. v. Ramirez, 824 S.W.2d 558 (Tex.1992) (per curiam) (granting mandamus to preclude disclosure of corporate tax returns on the basis of undue burden and unnecessary expense, not privilege).[8]
A fourth exception, based on Transamerican Natural Gas Corp. v. Powell, *853 811 S.W.2d 913 (Tex.1991, orig. proceeding), is described when the trial court imposes "discovery sanctions ... precluding a decision on the merits of a party's claims... unless the sanctions are imposed simultaneously with the rendition of a final, appealable judgment." At 843 (emphasis deleted). The majority falsely suggests that today's standard creates a symmetry with Transamerican. Unlike Transamerican, which treated the striking of a petition in the same manner as the entry of a default judgment, this ruling creates a double standard. Unlike Transamerican, which involved a readily-perceptible wrong such as an order of dismissal, a determination of whether hidden documents "go to the heart of a party's case," at 843, involves significant uncertainties.
More importantly, Transamerican was issued at a time when the announced policy of this court was to deter abuses of discretion without regard to whether discovery was granted or denied. A wide spectrum of sanction orders arising from discovery rulings are immediately appealable. See Braden v. Downey, 811 S.W.2d 922 (Tex. 1991, orig. proceeding). Superimposing Transamerican and Braden on today's double standard sends a clear message to the rare trial court that would impose significant penalties on those who obstruct discovery with deceit and delaybe careful. There is no real danger of immediate and genuine appellate examination of an order denying discovery, but there is a constant threat of appellate review of an order granting discovery or imposing meaningful sanctions on obstructionists. Once again the majority provides an incentive for concealment.
The remaining two situations address the wrongful denial of discovery, and constitute a narrow path in the woods compared to the expressway for resisting discovery constructed in the previous four exceptions. Mandamus is possible when
the missing discovery cannot be made part of the appellate record, or the trial court after proper request refuses to make it part of the record, and the reviewing court is unable to evaluate the effect of the trial court's error on the record before it.
At 843-844. The quick fix of including materials in the appellate record is both ingenious and ingenuous. It has the immediate "benefit" of excluding a great number of errors in the discovery area from mandamus review. As the majority in fact recognizes, "this situation should only rarely arise." At 844.[9] And if it ever does, the majority guarantees that no relief will be forthcoming, by directing that the reviewing court
carefully consider all relevant circumstances, such as the claims and defenses asserted, the type of discovery sought, what it is intended to prove, and the presence or lack of other discovery, to determine whether mandamus is appropriate.
At 844. Within these constraints, there will always be a readily available excuse to deny both discovery and mandamus.
In most cases the materials can be boxed up, file-stamped, and sent to the appellate court. How this will accomplish anything more than cluttering the judicial chambers is quite another matter. No clue is given as to how to resolve the obvious difficulties inherent in appellate determination, without any effective argument and analysis by counsel, of whether each item would have affected the result. Moreover, this approach improperly requires courts of appeals to act as juries while denying to the true fact-finder evidence that may be highly *854 relevant to the proceeding. This distrust of juriesof ordinary people resolving factual disputesis increasingly reflected in the majority's decisions.[10]
The only hope for review of a trial court's order denying discovery is upon proof that a claim has been "vitiated or severely compromised by the trial court's discovery error." At 843. It must be shown "that the trial would be a waste of judicial resources," at 843, and that "a denial of discovery [goes] to the heart of a party's case." At 843. It is far from clear whether these encompass one or three different standards. What is clear is that few cases, if any, will satisfy whatever standard is applied.
The majority offers no example of a case in which a party has ever met such a heavy burden. Apparently an applicant for mandamus in this court must confess that, without the discovery sought, the trial court should and must direct a contrary verdict. Any semblance of a chance at prevailing prevents a determination that the trial would be a "waste of judicial resources" or that the discovery denied goes "to the heart of a party's case." While this situation may theoretically arise in the future, it will be most unlikely. Nor is there any explanation of how a party can be expected to show such a probability without having any of the materials in question. We have previously recognized the hardship inherent in showing need for documents when their contents are unknown. State v. Lowry, 802 S.W.2d 669, 673 (Tex.1991) ("It is difficult for the [relators] to make a more particularized showing of need for these documents, the contents of which are unknown to them.").
Application of today's font of mandamus law to the Walkers' situation is most revealing. The majority summarily concludes that the trial court's misapplication of the law to deprive them of relevant evidence "does [not] vitiate or severely compromise the Walkers' ability to present a viable claim." At 844. Most ironically, today's announcement imposes one type of double standard on top of another alleged double standard. The Walkers claim they have uncovered a double standard at a taxpayer-financed institution that encourages faculty to defend those accused of medical malpractice while discouraging professional advice on behalf of the alleged victim. It is the merits of this revelation that the majority so eagerly seals away from both the Walkers and the public.
Fully aware of the impact of expert credibility on the outcome of much medical malpractice litigation, the majority denies the Walkers the very information that could perhaps demonstrate the bias of a key witness. An official blessing is thus provided for trial court action that may have a material, adverse effect on their ability to present a viable case. Having now learned that the denial of impeachment evidence is never susceptible to mandamus, it remains to be seen what other critical information will next be similarly viewed as unimportant to this majority.
While the nature of the double standard approved by today's writing requires that this dissent focus on wrongful denials, I recognize that the wrong can be every bit as real from improper grants of discovery. As a practical matter there is probably less danger that a trial judge will capriciously ignore properly established objections and privileges to accord too much information instead of too little. Nevertheless, I favor the use of mandamus to control abuse without regard to how it occurs or whom is helped. What I deplore is the discrimination which the majority officially substitutes for even-handedness. Scholars viewing *855 the so-called "Walker mandamus standard" should recognize that it is not a standard but an excuse for ignoring wrongdoing.
After today's decision, discovery disputes will no longer be resolved on a level playing field. I believe that mandamus should be available to correct any trial court abuse concerning a subject that is important to the jurisprudence of the state and which substantially affects rights of an aggrieved party. If this requisite is satisfied, relief should be accorded without regard to whether the trial court has granted or denied discovery.

VI.
In supporting today's opinion, Justice Gonzalez insists that we must stem what he claims is an alarming increase in the number of mandamus filings. At 844-846 (Gonzalez, J., concurring). The view that "the sky is falling" is best reflected in the gruesome statistics and conclusions of his dissenting opinion in Joachim v. Chambers, 815 S.W.2d 234, 241 (Tex.1991). See also Jampole, 673 S.W.2d at 578 (Barrow, J., dissenting); cf. C.L. Ray & M.R. Yogi McKelvey, The Mandamus Explosion, 28 S.Tex.L.Rev. 413, 413-14 (1987).
Blaming an ever-increasing caseload for the Texas courts on the advent of the discovery mandamus is wholly insupportable. These petitions most often present emergency situations requiring expedited review and, consequently, are frequently viewed as a thorn in the side of appellate courts. See Review of Discovery Orders at 1059 n. 99. But I cannot agree that justice should be denied or delayed solely to accommodate appellate judges.
Recent studies have debunked the myth of the mandamus explosion. The Joachim dissent, to which Justice Gonzalez once again points with pride today, is based upon an analysis that fails to segregate filings arising from discovery disputes. A more detailed study of Supreme Court experience during a period of more than ten years correctly concluded that:
[I]nterlocutory review of discovery orders... has [had] a positive effect.... The increase [in appellate caseloads] has been an extremely small and manageable one....
.....
The numbers, then, suggest that while the availability of interlocutory review of discovery orders added cases to the appellate docket, interlocutory review has not added a large or burdensome number of cases.
Review of Discovery Orders at 1047, 1059.
The fact is that most petitions are denied, with fewer than 3% granted by us during fiscal year 1991. Most of these were handled expeditiously, with over half resolved within one month of filing. Moreover, Justice Gonzalez completely ignored the fact that mandamus requests in this court actually decreased over the last three years. There were 202 of these in fiscal 1991, down from 257 and 258, respectively, in fiscal 1989 and 1990. Although the court's overall workload is expanding, the contribution of mandamus filings is certainly not uncontrollable.[11] "In deciding whether courts should permit interlocutory *856 review in specific cases, judges and commentators tend to emphasize the needs of court administration over the needs of the litigants." Id. at 1049. While cutting off the right to mandamus review when discovery is denied may reduce the appellate workload, the result will be a significant decline in the quality of justice. The inconvenience caused by the unexpected arrival of a petition that often demands immediate action is the price paid "to assure that ... trial proceedings are fair and equitable to all concerned parties.... `[W]e must not sacrifice justice upon the altar of expediency.' " Mandamus Review of Disclosure Orders at 422 (quoting David W. Holman & Byron C. Keeling, Disclosure of Witnesses in Texas: The Evolution and Application of Rules 166b(6) and 215(5) of the Texas Rules of Civil Procedure, 42 Baylor L.Rev. 405, 458 (1990)) (emphasis added).

VII.
The majority announces here not a standard, but a pseudo-standard. In reality, the rule is little more than "how can we help those whom we want to help?" The only true precedent for this is Terrazas v. Ramirez, 829 S.W.2d 712 (Tex.1991), where Republican relators in districting were accorded relief in the Supreme Court never sought in any other forum. This "triple R exception to mandamus," id. at 760-61 (Mauzy, J., dissenting), only presages the continued pursuit of this goal.
If doubts remain as to the one-sidedness of the standard announced today, its application to currently pending cases should resolve them. See, e.g., Remington Arms Co. v. Canales, No. D-1867, 35 Tex.S.CtJ. 245 (Dec. 13, 1991) (trial court order which found documents relating to firearm safety relevant and required their production stayed despite no timely response or objection being made); Eli Lilly & Co. v. Marshall, No. D-1827, 35 Tex.S.CtJ. 168, 354 (Dec. 3, 1991 and Jan. 23, 1992) (stays of trial court order directing production of information relating to the drug Prozac); see id. at 189 (Order Granting Leave to File Petition for Writ of Mandamus) (Doggett, J., dissenting); Valley Baptist Medical Center v. Bennett, No. D-1193, 34 Tex. S.CtJ. 668 (June 18, 1991) (stay issued to protect hospital from disclosure of materials relating to policy of informing patients of risk of treatment), and 35 Tex.S.CtJ. 452 (Feb. 12, 1992) (motion for leave to file granted). One interested in verifying the true meaning of the majority's carefully chosen words will do well to observe how the court actually disposes of each of these matters.

VIII. CONCLUSION
In an apparent attempt to cope with a false "mandamus explosion," today's opinion has offered us an explosion of another typea reverberating detonation of this court's prior rulings. True the majority has considerable experience in disregarding precedent as merely a lifeless thing of the past. See Edgewood III, 826 S.W.2d at 516, 517 (Doggett, J., dissenting); Terrazas, 829 S.W.2d at 739 (Mauzy, J., dissenting); Stewart Title Guaranty Co. v. Sterling, 822 S.W.2d 1, 12 (Tex.1991) (Doggett, J., dissenting). But a dozen or more Texas Supreme Court authorities and even more rulings from the courts of appeals cut down at one time is not a modest accomplishment. Precedent, no matter how voluminous or how well-established, will clearly not restrain this majority from accomplishing its preconceived social policy objectives.
Through both deed and now word, the majority invites a true explosion in mandamus filings. What does an attorney whose client faces the possibility of a judgment for significant damages have to lose from accepting the beneficence of a majority of this court ever willing to serve as protector of the privileged? Will a deposition site other than that ordered by the trial court *857 be more costly and inconvenient to the claimant? Get a stay from the Texas Supreme Court, even if your petition is still pending in the court of appeals. See Continental Can Co. v. Wittig, No. D-2015, 35 Tex.S.CtJ. 355, 1992 WL 17415 (Jan. 29, 1992) (stay of trial court order directing engineering employee of products liability defendant to be deposed in Houston rather than Chicago even though mandamus petition was pending in court of appeals). Did the trial court resolve a conflict in deposition schedules in a manner unacceptable to an insurance company? Don't worry, the Texas Supreme Court will stay proceedings even without bothering to get a response from the affected judge. See Cigna Corp. v. Spears, No. D-2069, 35 Tex.S.CtJ. 463 (Feb. 19, 1992). Any attorney whose client desires to make more difficult access to information that will jeopardize its credibility, suggest its liability or defeat its defenses would be foolish to accept a trial court discovery order. A majority of the Texas Supreme Court is ready and willing to interfere for the asking.
The ripple effect created by today's refusal to accord mandamus review to pretrial discovery orders will swell to tidalwave proportion, and sweep before it any hope of fair and consistent application of our Texas discovery rules. In many cases it will leave buried in the sand any possibility of trials directed by the full and truthful revelation of the underlying facts. Juries will be forced to resolve critical disputes based not on truths but rather upon whatever half-truths can be discovered. Left in the wreckage on the beach will be the tattered remains of the many prior decisions of this court and others that viewed litigation as a search for truth in which fair and prompt appellate review of an order denying discovery was vital.
MAUZY, J., joins in this dissenting opinion.
GAMMAGE, Justice, dissenting.
I dissent. Today's decision departs from previous instances where this court has provided mandamus relief to correct a wrongful denial of discovery, and labors too hard to conclude that appeal is an adequate remedy for a party who is denied adequate discovery.
I would hold that mandamus is available to correct a trial court error which negatively and materially affects the right of aggrieved parties to adequately present their cases, whether the particular party is seeking discovery or resisting it. See Iley v. Hughes, 158 Tex. 362, 368, 311 S.W.2d 648, 652 (1958); see also Elizabeth G. Thornburg, Interlocutory Review of Discovery Orders: An Idea Whose Time Has Come, 44 Sw.LJ. 1045 (1990). In the case before us, the trial court's denial of discovery has a material and adverse effect on the Walkers' ability to present their case. The information they seek could impugn the credibility of key expert witnesses at trial. Because their medical malpractice claim, like all such claims, will likely stand or fall on the credibility of the expert witnesses, I would hold that the Walkers are entitled to the information they seek, and that relief by appeal is inadequate.
Discovery is the "linchpin of the search for truth," and "[ajffording parties full discovery promotes the fair resolution of disputes by the judiciary." State v. Lowry, 802 S.W.2d 669, 671 (Tex.1991). Today the court removes and disposes of that "linchpin" and abandons enforcement of fair and adequate discovery. Because I believe that mandamus relief should be readily available when a court allows either too much or too little discovery, I dissent.
NOTES
[1]  St. Paul contends that the Walkers' request for mandamus relief is barred by laches since the Walkers delayed almost two years before seeking to compel production. Because we find that the Walkers have failed to establish the requirements for mandamus relief, we do not reach this issue.
[2]  The court also sustained Aetna's motion to quash, holding that the discovery requested was improper under the investigation exemption, the attorney-client privilege, and the work-product privilege. The Walkers do not complain to us about this ruling.
[3]  Even if no evidence had been presented, the Walkers would have had the burden of filing an affidavit so stating. See Barnes v. Whittington, 751 S.W.2d 493, 495 (Tex.1988) ("The undisputed fact that no testimony was adduced at any of the hearings, as set forth in the affidavit of relator's counsel, satisfies the relator's burden under Rule 121.").
[4]  The records sought in Russell included, among others:

(2) All appointment books maintained by [the expert physician] during 1969;
(3) All statements, listings, ledgers, or other books showing the accounts receivable of [the expert physician] during 1969;
(4) All deposit slips or tickets showing deposits into bank accounts of [the expert physician] during 1969;
(5) All statements, listings, ledgers, journals, or other books showing receipt of payments, either in cash, by check or by any other means [by the expert physician] during 1969;
(6) All statements of account or bills for services rendered [by the expert physician] during 1969;
(7) All accounting ledgers, journals or other books of account of [the expert physician] maintained during 1969; and
(8) All financial statements showing income and expenses of [the expert physician] during 1969.
452 S.W.2d at 435.
[5]  Evidence of bias is not admissible if the witness "unequivocally admits such bias or interest" at trial. Tex.R.Civ.Evid. 613(b). To date, however, Dr. Gilstrap has not admitted any bias, but rather has flatly denied it. In this situation, such evidence should be discoverable.
[6]  We do not decide whether the documents were properly discoverable, only that the trial court erred in denying discovery based solely on Russell. If the Walkers sought the documents solely to attack the credibility of Dr. Gilstrap by showing that his deposition testimony was untrue, for instance, the information would probably not be reasonably calculated to lead to the discovery of admissible evidence. See Tex. R.Civ.Evid. 608(b). ("Specific instances of the conduct of a witness [other than criminal convictions], for the purpose of attacking ... his credibility, may not be ... proved by extrinsic evidence.").
[7]  Additionally, this Court will not grant mandamus relief unless we determine that the error is of such importance to the jurisprudence of the state as to require correction. Cf. Tex.Gov't Code § 22.001(a)(6); Tex.R.App.P. 140(b). This issue, however, is properly resolved in deciding whether to grant leave to file the petition, not in its disposition.
[8]  See, e.g., TransAmerican Natural Gas Corp. v. Powell, 811 S.W.2d 913, 919 (Tex.1991) (imposition of discovery sanctions); Schultz v. Fifth Judicial District Court of Appeals, 810 S.W.2d 738, 739 n. 4 (Tex.1991) (refusal to enforce turnover order by contempt); Joachim v. Chambers, 815 S.W.2d 234, 240 (Tex.1991) (refusal to bar judicial officer from testifying as expert witness); Hooks v. Fourth Court of Appeals, 808 S.W.2d 56, 59-60 (Tex.1991) (refusal to grant nonsuit); Bell Helicopter Textron, Inc., v. Walker, 787 S.W.2d 954, 955 (Tex.1990) (refusal to dismiss for lack of subject-matter jurisdiction); Champion Intl Corp. v. Twelfth Court of Appeals, 762 S.W.2d 898, 899 (Tex.1988) (grant of new trial); Stringer v. Eleventh Court of Appeals, 720 S.W.2d 801, 801-02 (Tex.1986) (imposition of discovery sanction); Johnson v. Fourth Court of Appeals, 700 S.W.2d 916, 917 (Tex. 1985) (grant of new trial); Abor v. Black, 695 S.W.2d 564, 566 (Tex. 1985) (denial of plea in abatement); State v. Walker, 679 S.W.2d 484, 485 (Tex. 1984) (refusal to reinstate temporary injunction); Pat Walker & Co. v. Johnson, 623 S.W.2d 306, 309 (Tex.1981) (refusal to extend time for filing statement of facts); State Bar of Texas v. Heard, 603 S.W.2d 829, 833 (Tex.1980) (refusal to suspend attorney); Pope v. Ferguson, 445 S.W.2d 950, 953 (Tex. 1969) (refusal to dismiss criminal case pending against relator), cert, denied, 397 U.S. 997, 90 S.Ct. 1138, 25 L.Ed.2d 405 (1970); Crane v. Tunks, 160 Tex. 182, 190, 328 S.W.2d 434, 439 (1959) (discovery order); Iley v. Hughes, 158 Tex. 362, 367-68, 311 S.W.2d 648, 652 (1958) (bifurcation of trial); Harrell v. Thompson, 140 Tex. 1, 1, 165 S.W.2d 81, 81 (1942) (restriction of oil and gas production by Railroad Commission); Ben C. Jones & Co. v. Wheeler, 121 Tex. 128, 130, 45 S.W.2d 957, 958 (1932) (refusal to enter judgment nunc pro tunc); Cleveland v. Ward, 116 Tex. 1, 14, 285 S.W. 1063, 1068 (1926) (refusal to enter judgment); Aycock v. Clark, 94 Tex. 375, 376-77, 60 S.W. 665, 666 (1901) (refusal to enter injunction); Screwmen's Benevolent Ass'n v. Benson, 76 Tex. 552, 555, 13 S.W. 379, 380 (1890) (expulsion of member from charitable corporation).
[9]  We recently held that a mandamus action was never required to preserve error on appeal. Pope v. Stephenson, 787 S.W.2d 953 (Tex.1990). We explained: "The decision not to pursue the extraordinary remedy of mandamus does not prejudice or waive a party's right to complain on appeal." Id. at 954.
[10]  Courts use a similar approach in determining whether a witness has properly invoked the Fifth Amendment privilege against self-incrimination. It is often impossible for a witness to prove that an answer might incriminate him without actually answering and thereby forfeiting the privilege. Therefore, rather than requiring actual proof of the privilege, courts sustain the privilege if it is "evident from the implications of the question, in the setting in which it is asked, that a responsive answer [might be incriminating]." Hoffman v. United States, 341 U.S. 479, 487, 71 S.Ct. 814, 818, 95 L.Ed. 1118 (1951).
[1]  If the records have relevance apart from their potential for impeachment, however, Russell does not bar discovery. See Ex Parte Shepperd, 513 S.W.2d 813, 816 (Tex.1974).
[1]  Billie Holiday, God Bless the Child (Okeh Records 1941) (words and music by Arthur Herzog, Jr. & Billie Holiday).
[2]  These entities rarely need information to prevail:

Even when an institutional litigant appears as a plaintiff suing an individual defendant as, for example, when a corporation sues an individual on a debt, the institutional litigant tends to already have the information needed to prove its case.
Review of Discovery Orders at 1070 n. 162. They are also less likely to requires information from an opponent to establish affirmative defenses. Id. at 1070.
[3]  With no appellate opinions setting forth appropriate limitations upon trial court discretion, "litigants may receive widely divergent rulings from different judges, even in the same geographical location." Id. at 1077. Proper use of mandamus discourages forum shopping to obtain a trial judge more likely to provide a more favorable ruling and allows for greater consistency and accountability:

[Such] review ... even[s] out inconsistencies in trial court rulings, and ... allows trial judges to operate with a more accurate understanding of the meaning of the discovery rules.... If the appellate court is consistent, it can fix disparities and inequities produced by the trial courts and promote consistency among the trial level decisionmakers.
Id. at 1047, 1077 (footnotes omitted).
[4]  Intermediate appellate courts have also recognized the importance of mandamus to avoid trial court abuse in improperly limiting or denying discovery. See, e.g., Kentucky Fried Chicken Natl Mgmt. Co. v. Tennant, 782 S.W.2d 318 (Tex.App.Houston [1st Dist.] 1989, orig. proceeding) (writ granted when discovery of plaintiffs psychiatric records denied); Foster v. Heard, 757 S.W.2d 464 (Tex.App.Houston [1st Dist.] 1988, orig. proceeding) (mandamus issued against trial court's denial of discovery of postaccident investigation report); Super Syndicate, Ltd. v. Salazar, 762 S.W.2d 749 (Tex.App. Houston [14th Dist.] 1988, orig. proceeding) (granting mandamus against trial court's denial of discovery of claims investigator's files); Goodspeed v. Street, 747 S.W.2d 526 (Tex.App. Fort Worth 1988, orig. proceeding) (trial court's denial of discovery of hospital records based on privilege without presentation of evidence overturned); Estate of Gilbert v. Black, 722 S.W.2d 548, 551 (Tex.App.Austin 1987, orig. proceeding) (denial of discovery of insurer's internal communications overturned on mandamus, despite argument that "mandamus is proper only [for] improperly ordered discovery of privileged material, not when the trial court has denied discovery."); Essex Crane Rental Corp. v. Kitzman, 723 S.W.2d 241 (Tex.App.Houston [1st Dist.] 1986, orig. proceeding) (writ granted to correct trial court's order quashing deposition); Velasco v. Haberman, 700 S.W.2d 729, 730 (Tex. App.San Antonio 1985, orig. proceeding) (mandamus appropriate "not only where the trial court order improperly grants discovery, but the writ may also issue where the trial court improperly limits or denies discovery."); Aztec Life Ins. Co. v. Dellana, 667 S.W.2d 911 (Tex. App.Austin 1984, orig. proceeding) (mandamus issued against trial court for denying discovery of claims files).
[5]  The majority identifies by name five cases in conflict with today's writing, declaring that: "We disapprove of Barker and Allen, and any other authorities," at 842, and "[we] disapprove of Cleveland, Crane, Jampole, and any other authorities," at 842, to the extent they conflict with the new Walker standard. Subsumed within the "other" designation are a great number of additional cases from this court and the courts of appeals that would grant to the Walkers relief when the trial court has clearly abused its discretion in denying discovery. The court's willingness to sweepingly erase whole unidentified categories of recent precedent is exemplified by their signing of a blank check: "any other authorities," meaning all other authorities, are now endangered.
[6]  The few cases citing Automatic Drilling do not expand its holding to that suggested by the court today. See Jampole, 673 S.W.2d at 574-75 ("We hold that discovery cannot be denied because of an asserted proprietary interest in the requested documents when a protective order would sufficiently preserve that interest."); Firestone Photographs, Inc. v. Lamaster, 567 S.W.2d 273, 278 (Tex.Civ.App.Texarkana 1978, no writ) ("[T]he claim of trade secrets ... does not necessarily defeat the right of discovery.").
[7]  James B. Sales, Pretrial Discovery in Texas Under the Amended Rules: Analysis and Commentary, 27 S.Tex.L.Rev. 305, 345-46 (1986), stating that:

Trade secrets ... are not, per se, exempt from discovery. The trial court is obligated to weigh the need for discovery against the interests on secrecy.... The need to protect the confidentiality of documents does not constitute an absolute bar to discovery....
[8]  Although also citing General Motors Corp. v. Lawrence, 651 S.W.2d 732 (Tex. 1983, orig. proceeding), as allowing mandamus relief from an allegedly burdensome trial court discovery order, the majority fails to note the very expansive discovery permitted in that case. The efforts of General Motors to limit discovery to results from tests performed on the particular type of truck and the particular type of impact involved in the subject incident were rejected, and it was directed to supply all impact test results for all types of trucks manufactured over a 23-years period.
[9]  If the trial court "refuses to make [the discovery] part of the record," At 843, presumably the only relief accorded under today's standard would be issuance of a writ directing inclusion of these materials.
[10]  See Caller Times Publishing Co. v. Triad Communications, 826 S.W.2d 576, 597-608 (Tex. 1992) (Doggett, J., dissenting) (addressing court's refusal to allow evidence of predatory intent); see also Greater Houston Transp. Co. v. Phillips, 801 S.W.2d 523, 527 (Tex.1990) (Doggett, J., dissenting); Crim Truck & Tractor Co. v. Navistar Intl Transp. Co., 823 S.W.2d 591, 596 & n. 1 (Tex.1992) (Mauzy, J., dissenting); Reagan v. Vaughn, 804 S.W.2d 463, 488 (Tex.1990) (Doggett, J., concurring and dissenting).
[11]                  Supreme Court Filings
         Year   Mandamus   All          Total Mandamus  Discovery
                Discovery  Mandamusand  Applications    as Percentage
                Orders     Filings      for Writ        of Total
   1979       24          129             933           2.6%
   1981       17           98             943           1.8%
   1989       51          257            1078           4.7%
   1991       64          202            1257           5.1%

Interlocutory Review of Discovery Orders at 1058-59; the 1989 and 1991 figures are derived from my review of court filings.
