                                IN THE

    SUPREME COURT OF THE STATE OF ARIZONA
                          STATE OF ARIZONA,
                              Petitioner,

                                   v.

           THE HONORABLE JERRY BERNSTEIN, JUDGE PRO
TEMPORE OF THE SUPERIOR COURT OF THE STATE OF ARIZONA, IN AND FOR
                    THE COUNTY OF MARICOPA,
                         Respondent Judge

  DOREEN LYNN HERMAN; RAMSEY TOHANNIE; ARMEN ASLAYAN; KEITH
  PORTER; MARA HALL; SHYLA ROTMIL; ROBERT R. FARINAS; KYMBERLY
     CROWLEY; JASON QUAN; MICHAEL DINOLA; KELLY LEWIS DAY,
                      Real Parties in Interest.

                          No. CV-14-0057-PR
                          Filed April 23, 2015

       Special Action from the Superior Court in Maricopa County
           The Honorable Jerry Bernstein, Judge Pro Tempore
                          No. CR2010-126778
                     VACATED AND REMANDED

             Opinion of the Court of Appeals, Division One
                 234 Ariz. 89, 317 P.3d 630 (App. 2014)
                         VACATED IN PART

COUNSEL:

W. Clifford Girard, Jr., Mark D. DuBiel, Lawrence Koplow, Joseph P. St.
Louis (argued), Phoenix, Attorneys for Doreen Lynn Herman, et al.

William G. Montgomery, Maricopa County Attorney, Lisa Marie Martin
(argued), Deputy County Attorney, Phoenix, Attorneys for State of Arizona

Bruce Washburn, Scottsdale City Attorney, Ken Flint, Assistant City
Prosecutor, Scottsdale, Attorneys for Amicus Curiae City of Scottsdale

Alan B. Kelly, Scottsdale, Attorney for Amicus Curiae Scottsdale Lincoln
Health Network
                    STATE V. BERNSTEIN (HERMAN)
                         Opinion of the Court


CHIEF JUSTICE BALES authored the opinion of the Court, in which VICE
CHIEF JUSTICE PELANDER, and JUSTICES BERCH, BRUTINEL, and
TIMMER joined.

CHIEF JUSTICE BALES, opinion of the Court:

¶1             Arizona Rule of Evidence 702 requires a trial court to act as a
gatekeeper to ensure that only reliable expert witness testimony is admitted
for the jury’s consideration. This case concerns the trial court’s role under
Rule 702(d) when a party contends that an expert has not properly applied
generally reliable principles or methods. We hold that courts, as
gatekeepers, should consider whether a methodology has been correctly
applied. But we conclude that errors in application should result in the
exclusion of evidence only if they render the expert’s conclusions
unreliable; otherwise, the jury should be allowed to consider whether the
expert properly applied the methodology in determining the weight or
credibility of the expert testimony.
                                      I.

¶2           Real parties in interest are eleven defendants charged with
aggravated driving under the influence. The Scottsdale Crime Laboratory
(“SCL”) tested each defendant’s blood for blood alcohol concentration
(“BAC”). As described by the court of appeals:

       To test the blood, the SCL used a Clarus 500 gas
       chromatograph serial number 650N9042003 manufactured by
       PerkinElmer (the 2003 Instrument), an autosampler, a
       personal computer and a printer. Stated simply, after
       calibration, several dozen vials are placed in the carousel of
       the 2003 Instrument. The vials contain blood samples (each
       individual has two samples tested at a time, with the second
       sample called a replicate) along with control samples. The
       vials are sampled, one by one, and analyzed by the 2003
       Instrument, a process that takes several hours. The data are
       then processed (creating graphs showing the chemical
       properties of the compounds tested for called
       chromatograms) and results are calculated and printed. The
       output is checked for consistency with expected results,
       control samples and quality controls, and replicates are

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                     STATE V. BERNSTEIN (HERMAN)
                          Opinion of the Court

       checked to make sure that results are within plus or minus
       five percent of each other according to SCL protocol. A
       second analyst then performs a technical review, which is
       followed by an administrative review.

State v. Bernstein, 234 Ariz. 89, 92 ¶ 2, 317 P.3d 630, 633 (App. 2014).

¶3            Defendants moved to exclude evidence of their BAC results
under Rule 702, arguing that the instrument had unresolved flaws that
undermined its reliability. They pointed primarily to “data drops,” a term
they use to describe the instrument’s occasional failure to produce any
results for a sample, mislabeling of vials, and emails among SCL staff
expressing concerns about the instrument.

¶4            After a seventeen-day evidentiary hearing held pursuant to
Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993), the court
found that “[n]o testimony has shown that any of the consolidated
defendants’ tests were inaccurate. The State, in fact, presented evidence to
the contrary.” Only one defendant’s test had been performed improperly,
and that sample was later rerun. The court also observed that “because [the
instrument] is non-conforming doesn’t necessarily mean the results are
inaccurate.”

¶5              The trial court then discussed the data drops, the mislabeling,
and the staff emails. The court found it significant that the instrument was
still being used even though the lab’s accreditation standards required non-
conforming instruments to be removed from service to evaluate a
malfunction. In the emails, SCL staff expressed concern that the cause of
the malfunctions had not been determined or the problem resolved, raising
potential legal issues. The court concluded that “[i]nherent in the concept
of reliability is confidence,” and that, in light of the emails, “confidence in
the reliability of [the instrument] is clearly undermined.”

¶6            Although the court found that the State met its burden under
Rule 702(a) through (c) for establishing the admissibility of the BAC results,
the court ruled that the State failed to show that the testing methodology
had been reliably applied as required by subsection (d). The court thus
excluded evidence of the results as to all defendants.



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                    STATE V. BERNSTEIN (HERMAN)
                         Opinion of the Court

¶7            The State petitioned for special action relief in the court of
appeals, which granted relief. Bernstein, 234 Ariz. at 100 ¶ 29, 317 P.3d at
641. The court of appeals focused on the data drops but concluded that
“[t]here was no showing . . . that such failures to provide test results meant
that usable BAC test results [that were] produced by the 2003 Instrument
were not reliable.” Id. at 98 ¶ 22, 317 P.3d at 639. The court thus held that
the State met its burden as to Rule 702(d) and vacated the trial court’s order
excluding the evidence. Id. at 100 ¶ 27, 317 P.3d at 641.

¶8             We granted review because the application of Rule 702(d) is a
recurring issue of statewide importance. We have jurisdiction pursuant to
Article 6, Section 5(3) of the Arizona Constitution and A.R.S. § 12-120.24.

                                      II.

¶9             We review the interpretation of court rules de novo, State v.
Salazar-Mercado, 234 Ariz. 590, 592 ¶ 4, 325 P.3d 996, 998 (2014), but we
review a trial court’s exclusion of evidence for an abuse of discretion, State
v. Davolt, 207 Ariz. 191, 209 ¶ 66, 84 P.3d 456, 474 (2004). An error of law
constitutes an abuse of discretion. Twin City Fire Ins. Co. v. Burke, 204 Ariz.
251, 254 ¶ 10, 63 P.3d 282, 285 (2003). Because Rule 702 mirrors its federal
counterpart, we may look to the federal rule and its interpretation for
guidance. Salazar-Mercado, 234 Ariz. at 592 ¶ 7, 325 P.3d at 998. As the
proponent of the expert testimony, the State bears the burden of
establishing its admissibility by a preponderance of the evidence. Id. at
593 - 94 ¶ 13, 325 P.3d at 999 - 1000.

                                     III.

¶10          Rule 702, which governs expert witnesses testimony,
provides that:

       A witness who is qualified as an expert by knowledge, skill,
       experience, training, or education may testify in the form of
       an opinion or otherwise if:

       (a) the expert’s scientific, technical, or other specialized
       knowledge will help the trier of fact to understand the
       evidence or to determine a fact in issue;


                                      4
                    STATE V. BERNSTEIN (HERMAN)
                         Opinion of the Court

       (b) the testimony is based on sufficient facts or data;

       (c) the testimony is the product of reliable principles and
       methods; and

       (d) the expert has reliably applied the principles and methods
       to the facts of the case.

¶11           The rule “recognizes that trial courts should serve as
gatekeepers in assuring that proposed expert testimony is reliable and thus
helpful to the jury’s determination of facts at issue.” Ariz. R. Evid. 702 cmt.
(2012). But the comment also observes that “[t]he trial court’s gatekeeping
function is not intended to replace the adversary system.” Id. Rather,
“[c]ross-examination, presentation of contrary evidence, and careful
instruction on the burden of proof are the traditional and appropriate
means of attacking shaky but admissible evidence.” Id.; cf. Daubert, 509 U.S.
at 596.

¶12           Daubert left unclear whether the particular application of a
generally reliable methodology should be assessed by the trial court as part
of its gatekeeper role or instead by the jury in determining the weight to
give expert testimony. Courts and commentators have continued to
suggest different approaches to the issue. See, e.g., United States v.
McCluskey, 954 F. Supp. 2d 1224, 1243 - 55 (D.N.M. 2013) (discussing cases);
29 Charles Alan Wright & Victor James Gold, Federal Practice & Procedure
§ 6266 (1st ed. 2014) (distinguishing between “broad” and “narrow” views
regarding the scope of the gatekeeping inquiry).

¶13            Rule 702(d), however, recognizes that a trial court must
consider whether an expert reliably applied the pertinent methodology
when expert testimony concerns the facts of a particular case. Cf. Salazar-
Mercado, 234 Ariz. at 593 ¶¶ 10-11, 325 P.3d at 999 (holding that “cold”
expert testimony not based on the facts of a case may be admissible if it
satisfies Rule 702(a) - (c)). Thus, the rule by its terms forecloses the
approach of leaving challenges to an expert’s application of a methodology
exclusively to the jury. Such challenges are instead a proper subject of the
trial court’s gatekeeping inquiry. But cf. United States v. Bonds, 12 F.3d 540,
563 (6th Cir. 1993) (holding, under earlier version of Federal Rule 702, that
“in general, criticisms touching on whether the lab made mistakes in
arriving at its results are for the jury”).

                                      5
                     STATE V. BERNSTEIN (HERMAN)
                          Opinion of the Court

¶14             But not all errors in the application of reliable principles or
methods will warrant exclusion. Rule 702 contemplates that expert
testimony can be “shaky” yet admissible. Ariz. R. Evid. 702 cmt. (2012).
“The overall purpose of Rule 702 . . . is simply to ensure that a fact-finder
is presented with reliable and relevant evidence, not flawless evidence.”
State v. Langill, 945 A.2d 1, 10 (N.H. 2008). Rule 702(d) “must be interpreted
and applied with some flexibility to encompass the multitude of scenarios
that may be presented and to maintain the division in function between the
fact-finder and gatekeeper.” Id.

¶15            Errors in the application of a generally reliable methodology,
therefore, should not serve to exclude evidence unless they are so serious
as to render the results themselves unreliable. See id. (“[I]t would be
unreasonable to interpret [Rule 702(d)] as requiring that a single flaw or
even multiple flaws in an expert’s application of a particular methodology
in all instances renders inadmissible the expert’s entire testimony.”). With
respect to test results, for example, the omission of a step necessary to
obtain valid results or a procedural misstep that plausibly could skew the
outcome might justify excluding the results and any opinion based on them.

¶16            Several courts have attempted to describe the point at which
errors in application warrant the exclusion of expert testimony. The Third
Circuit held that a trial judge “should only exclude evidence if the flaw is
large enough that the expert lacks ‘good grounds’ for his or her
conclusions.” In re Paoli R.R. Yard PCB Litig. (Paoli), 35 F.3d 717, 746 (3d Cir.
1994). In the Eighth Circuit, “[a]n alleged error in the application of a
reliable methodology should provide the basis for exclusion of the opinion
only if that error negates the basis for the reliability of the principle itself.”
United States v. Martinez, 3 F.3d 1191, 1198 (8th Cir. 1993); see also United
States v. Gipson, 383 F.3d 689, 697 (8th Cir. 2004) (“[O]utright exclusion of
the evidence in question is warranted only if the methodology was so
altered by a deficient application as to skew the methodology itself.”).
Although worded somewhat differently, the Eighth Circuit’s test is
essentially the same as the Third Circuit’s. See McCluskey, 954 F. Supp. 2d
at 1249.

¶17             We agree with this approach and that stated by the New
Hampshire Supreme Court: alleged flaws in the application of a reliable
methodology should not result in exclusion of evidence unless they “so
infect[ ] the procedure as to make the results unreliable.” Langill, 945 A.2d

                                        6
                    STATE V. BERNSTEIN (HERMAN)
                         Opinion of the Court

at 10 (quoting Martinez, 3 F.3d at 1198); cf. Fed. R. Evid. 702 Advisory
Comm. Notes (2000) (noting that changing or misapplying a reliable
methodology so that analysis is unreliable will render expert testimony
inadmissible (citing Paoli, 35 F.3d at 745)).

¶18            Whether errors in application render evidence unreliable will
not always be clear. In close cases, the trial court should allow the jury to
exercise its fact-finding function, for it is the jury’s exclusive province to
assess the weight and credibility of evidence. State v. Clemons, 110 Ariz. 555,
556 – 57, 521 P.2d 987, 988 – 89 (1974). “[A]s long as an expert’s scientific
testimony rests upon good grounds, . . . it should be tested by the adversary
process—competing expert testimony and active cross-examination—
rather than excluded from jurors’ scrutiny for fear that they will not grasp
its complexities or satisfactorily weigh its inadequacies.” Langill, 945 A.2d
at 11 (quoting United States v. Vargas, 471 F.3d 255, 265 (1st Cir. 2006)).

                                     III.

¶19            The parties do not dispute that gas chromatography is a
reliable methodology for determining BAC and that expert testimony on
that topic is relevant and helpful, so the State has met its burden as to Rule
702(a) through (c). Relying on Rule 702(d), defendants argue that their BAC
results must be excluded because the instrument’s faults establish that the
methodology was not reliably applied. The trial court properly considered
defendants’ challenges as part of its gatekeeping inquiry. But the court
applied the wrong legal standard under Rule 702(d) and thereby abused its
discretion in excluding the evidence. See Twin City Fire Ins. Co., 204 Ariz. at
254 ¶ 10, 63 P.3d at 285.

¶20             The trial court observed that “[i]nherent in the concept of
reliability is confidence,” and that the emails among SCL staff expressing
concern about the instrument undermined confidence in its reliability. The
emails did not express doubt about the reliability of the results for
particular samples, but instead related concerns that the data drops
remained unresolved and might become subject to legal challenge. The trial
court misapplied Rule 702(d) by concluding that the staff’s general concerns
established that the instrument’s methodology had not been reliably
applied with respect to the particular BAC results at issue.



                                      7
                    STATE V. BERNSTEIN (HERMAN)
                         Opinion of the Court

¶21           The trial court also explained its ruling by noting the data
drops, the mislabeling, and the laboratory’s failure to remove the
instrument from service. But the fact that the instrument here sometimes
failed to produce a reading does not itself imply that the results it did
generate were inaccurate. (A different conclusion would result if an
instrument did not accurately measure a known standard or failed to
produce consistent results for replicate samples within a required range.)
And the State presented evidence that incidents of mislabeling could
readily be corrected based on the printing sequence, and no evidence
suggests that the defendants’ samples were misidentified. The record does
not show that the identified errors rendered the results of the defendants’
tests unreliable; instead, as the trial court acknowledged, the State
presented evidence supporting the accuracy of those results. As to the
defendants’ results, the State met its burden under Rule 702(d) of showing
that gas chromatography had been reliably applied to analyze BAC.

¶22          This is not to say that the malfunctions or the lab’s failure to
resolve them are irrelevant. The jury may consider the instrument’s
malfunctioning and the laboratory staff’s related concerns when assessing
the weight or credibility of the test results. This conclusion recognizes that
“[c]ross-examination, presentation of contrary evidence, and careful
instruction on the burden of proof are the traditional and appropriate
means of attacking shaky but admissible evidence.” Ariz. R. Evid. 702 cmt.
(2012).

                                     IV.

¶23           We vacate the trial court’s order excluding evidence of the
BAC results, vacate ¶¶ 19 - 28 of the court of appeals’ opinion, and remand
the case to the trial court for further proceedings.




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