
556 N.W.2d 524 (1996)
219 Mich. App. 456
SCHOOL DISTRICT FOR THE CITY OF ADRIAN, Albion Public Schools, Allegan County Intermediate School District, Alma Public Schools, Alpena Public Schools, Birch Run Area Schools, Bridgman Public School District, Calhoun Intermediate School District, Carman-Ainsworth Community Schools, Carrollton Public Schools, Carson City-Crystal Area Schools, Central Montcalm Public Schools, Charlotte Public Schools, Clarkston Community Schools, Coloma Community Schools, Constantine Public Schools, Dewitt Public Schools, Dickinson-Iron Intermediate School District, East China School District, School District of The City of East Lansing, Eaton Intermediate School District, Edwardsburg Public Schools, Fenton Area Public Schools, Fruitport Community Schools, Genessee Intermediate School District, Grand Ledge Public Schools, Greenville Public Schools, Hart Public Schools, Holland Public Schools, Houghton Lake Community Schools, Hudson Area Schools, Ionia Public Schools, Jenison Public Schools, Lenawee Intermediate School District, Madison School District, Marquette Public Schools, Marquette-Alger Intermediate School District, Mayville Community Schools, Mio-Ausable Schools, Morenci Area Schools, Mt. Morris Consolidated School District, Muskegon Area Intermediate School District, Negaunee Public Schools, Newaygo Intermediate School District, Niles Community Schools, North Branch Area Schools, Northview Public Schools, Oscoda Area Schools, Otsego Public Schools, Shelby Public Schools, Shiawassee Intermediate School District, South Lyon Community Schools, St. Joseph Public Schools, Standish-Sterling Community Schools, Tuscola Intermediate School District, Vassar Public Schools, Washtenaw Intermediate School District, and West Ottawa Public Schools, Petitioners-Appellants,
v.
MICHIGAN PUBLIC SCHOOL EMPLOYES' RETIREMENT SYSTEM and Michigan Public School Employees' Retirement Board, Respondents-Appellees, and
Michigan Education Association, Amicus-Curiae.
Docket No. 178195.
Court of Appeals of Michigan.
Submitted May 21, 1996, at Lansing.
Decided October 15, 1996, at 9:00 a.m.
Released for Publication December 23, 1996.
*525 Thrun, Maatsch and Nordberg, P.C. by Donald J. Bonato and Philip A. Erickson, Lansing, for petitioners-appellants.
Frank J. Kelley, Attorney General, Thomas L. Casey, Solicitor General, and Michael J. Moquin, Assistant Attorney General, for respondents-appellees.
White, Przybylowicz, Schneider & Baird, P.C. by Karen Bush Schneider, Okemos, for amicus curiae Michigan Education Association.
Before MARKEY, P.J., and McDONALD and M.J. TALBOT,[*] JJ.
PER CURIAM.
Petitioners, public school districts, appeal by leave granted from the trial court's order affirming respondent Michigan Public School Employees' Retirement Board's declaratory ruling that public school employers must pay contributions to defendant Michigan Public School Employees' Retirement System (MPSERS) for members who are receiving worker's compensation benefits and that those members are entitled to accrue retirement benefits and obtain service credit while receiving worker's compensation benefits. With respect to contributions due and owing before June 12, 1996, we reverse and remand this case to the trial court for further proceedings. See 1996 P.A. 268, amending, in part, what was formerly M.C.L. § 38.1304(1); M.S.A. § 15.893(114)(1).
Petitioners first assert on appeal that respondent board erred in interpreting the Public School Employees Retirement Act, as amended, M.C.L. § 38.1301 et seq.; M.S.A. § 15.893(111) et seq., in a manner that permits worker's compensation benefits to be considered as compensation pursuant to the act. We agree.
In reviewing an administrative agency's rulings, we will set those rulings aside only if they violate the constitution or a statute or are affected by substantial and material errors of law. M.C.L. § 24.306(1)(a) and (f); M.S.A. § 3.560(206)(1)(a) and (f); Barker Bros. Construction v. Bureau of Safety & Regulation, 212 Mich.App. 132, 136, 536 N.W.2d 845 (1995). "Longstanding and invariant administrative agency interpretations of a statute that the agency is empowered to administer are entitled to great deference by the courts, absent a contrary logical reading of the statute." Id. An administrative interpretation of a statute is not conclusive, however, and cannot overcome a logical reading of the statute. Majurin v. Dep't of Social Services, 164 Mich.App. 701, 704, 417 N.W.2d 578 (1987).
In the case at bar, we believe that the clear and unambiguous language of the retirement act before June 12, 1996, did not *526 provide that MPSERS members receiving worker's compensation benefits were entitled to retirement service credit. Section 4(1) of the retirement act before its amendment by 1996 P.A. 268, formerly M.C.L. § 38.1304(1); M.S.A. § 15.893(114)(1), defined compensation as follows:
"Compensation" means the remuneration earned by a member for service performed as a public school employee. If part of a member's remuneration is not paid in money, the retirement board shall fix the value of that part of the remuneration not paid in money. Compensation includes, on a current basis, investments made in a tax sheltered annuity for a public school employee as remuneration for service under this act. The remuneration shall be valued at the amount of money actually paid into the annuity. Compensation includes all amounts deducted from the pay of a public school employee, including amounts deducted pursuant to the member investment plan. Compensation includes longevity pay, overtime pay, vacation pay, and holiday pay while absent from work, sick leave pay while absent from work, and items of deferred compensation, exclusive of employer contributions to the retirement system. Compensation does not include terminal payments for unused sick leave, annual leave, bonus payments, hospitalization insurance and life insurance premiums, other fringe benefits paid by and from the funds of employers of public school employees, and remuneration paid for the specific purpose of increasing the final average compensation. [Emphasis added.]
According to petitioners, compensation was defined as remuneration for services performed, so the period that a member was receiving worker's compensation benefits had to be considered as time when services were performed and that a member was entitled to service credit while receiving this form of remuneration. We disagree.
First, M.C.L. § 38.1387; M.S.A. § 15.893(197) provides that a member who becomes totally and permanently disabled from a work-related injury may receive service credit for the time that the member is injured and receives worker's compensation benefits if the member recovers and returns to work. Second, M.C.L. § 38.1390; M.S.A. § 15.893(200) provides that if a member dies from a work-related injury for which the member receives worker's compensation benefits, the surviving spouse is entitled to a retirement allowance that is computed as if the deceased member had retired on the date preceding the member's death. Both of these provisions within the retirement act expressly provide for service credit when a member is not working for a public school because of a work-related injury, is receiving worker's compensation benefits, and either (a) has been permanently injured and is later able to return to work or (b) dies as a result of injury or illness arising out of and in the course of the member's service. If the Legislature had intended to give all members service credit for all the times a member received worker's compensation benefits, then these specific exceptions would be rendered nugatory. Michigan Employment Security Comm v. Westphal, 214 Mich.App. 261, 263-264, 542 N.W.2d 360 (1995). Indeed, because Michigan recognizes the principle of expressio unius est exclusio alterius (express mention in a statute of one thing implies the exclusion of other similar things), we find that service credit should not have been available for members who failed to qualify for such credit under these two specific statutory provisions. See Jennings v. Southwood, 446 Mich. 125, 142, 521 N.W.2d 230 (1994); Stowers v. Wolodzko, 386 Mich. 119, 133, 191 N.W.2d 355 (1971).
We reach this decision by keeping in mind the fundamental rule of statutory construction: to ascertain the purpose and intent of the Legislature in enacting a statute. Farrington v. Total Petroleum, Inc., 442 Mich. 201, 212, 501 N.W.2d 76 (1993); In re Schnell, 214 Mich.App. 304, 309, 543 N.W.2d 11 (1995). Contrary to respondents' assertions, we cannot speculate concerning the Legislature's probable intention unless that intention is expressed in the words of the statute. Here, although the term "sick leave pay while absent from work" could, when reviewed in a vacuum, equate with worker's disability compensation, we find no evidence that the Legislature intended this *527 interpretation before expressly so stating as of June 12, 1996. As always, we will not engage in judicial construction of a statute where reasonable minds cannot differ with respect to the meaning of the statute or where the plain and ordinary meaning of the statutory language is clear. Westphal, supra. Even assuming, arguendo, that we must apply a reasonable construction of the statute in light of the purpose of the statute, we would reach the same conclusion. Id.
Indeed, in Beneteau v. Detroit Free Press, 117 Mich.App. 253, 259-261, 323 N.W.2d 498 (1982), this Court recognized a distinction between sick pay, which is a form of compensation from an employer to an employee, and worker's compensation benefits, which are statutorily mandated benefits paid to employees injured on the job. This Court refused to permit the employer to offset sick pay against worker's compensation payments due to the plaintiff upon finding that the sick leave benefits were unrelated to worker's compensation benefits. Accordingly, we do not accept respondents' assertions that sick leave pay and worker's compensation benefits are synonymous for purposes of the retirement act. As often happens, we have been asked in this case to interpret creatively the clear language of a statute, but we must decline defendants' invitation to do so. The result here is required by the statute, and respondents' arguments are best addressed to the Legislature. See Miller v. Riverwood Recreation Center, Inc., 215 Mich.App. 561, 546 N.W.2d 684 (1996).
In fact, our conclusion is further buttressed by the Legislature's recent addressing of this precise issue by the passage of 1996 P.A. 268, which became effective on June 12, 1996. Section 3a(2)(f) of 1996 P.A. 268, M.C.L. § 38.1303a(2)(f); M.S.A. § 15.893(113a)(2)(f), redefines the term "compensation" that was formerly found in M.C.L. § 38.1304(1); M.S.A. § 15.893(114)(1) to specifically include within the definition of "sick leave" weekly worker's disability compensation payments, as follows:
Compensation includes salary and wages and all of the following:

* * * * * *
(f) Pay for vacation, holiday, and sick leave while absent from work. As used in this subdivision, "sick leave" includes weekly worker's disability compensation payments received for personal injury in the employ of and while employed by a reporting unit. [Emphasis added.]
Accordingly, in light of the plain and ordinary language of what is now M.C.L. § 38.1303a; M.S.A. § 15.893(113a), the Legislature intends that MPSERS members will earn service credit while receiving worker's compensation benefits and that public school districts must pay contributions to MPSERS for members who receive worker's compensation benefits on or after June 12, 1996. See Westphal, supra.
We believe that the 1996 amendment of M.C.L. § 38.1304(1); M.S.A. § 15.893(114)(1) has, in effect, proved petitioners' case in this appeal. Petitioners had no statutory duty to contribute to the MPSERS for teachers receiving worker's compensation before June 12, 1996. Other school districts may have voluntarily treated worker's compensation benefits as compensation in the past, even though the statute was silent in this respect. Nevertheless, petitioners challenged respondents' desire to seek similar compliance from them in the absence of statutory support, and we find that their challenge has merit. Absent evidence of a prior legislative intent to treat worker's compensation as "sick leave" and "compensation" under the statute, petitioners did not err in refusing to make contributions into the MPSERS retirement fund regarding teachers who were receiving worker's compensation benefits. Moreover, given the lack of any language regarding any retroactive effect of 1996 P.A. 268 and the effect that this statutory amendment will have on MPSERS members' substantive rights, we believe that 1996 P.A. 268 must be given prospective application only. Ramsey v. Michigan Underground Storage Tank Financial Assurance Policy Bd., 210 Mich.App. 267, 269-270, 533 N.W.2d 4 (1995). Accordingly, 1996 P.A. 268 does not alter our conclusion here, but its existence does change petitioners' obligations to the MPSERS as of June 12, 1996.
*528 Petitioners also assert that respondent board did not comply with the rule-making requirements of the Administrative Procedures Act, M.C.L. § 24.201 et seq.; M.S.A. § 3.560(101) et seq., when it adopted the new policies supporting respondent board's declaratory ruling. We disagree. The declaratory ruling and policies adopted by MPSERS were not "rules" as defined by the APA. Specifically, M.C.L. § 24.207(i) and (j); M.S.A. § 3.560(207)(i) and (j) expressly exclude from the definition of the term "rule" both declaratory rulings and decisions "by an agency to exercise or not to exercise a permissive statutory power, although private rights or interests are affected." Thus, we find no error.
Accordingly, we reverse the trial court's order affirming respondent board's determination that member employees should receive service credit toward their retirement while those employees were recuperating from a work-related injury and that petitioners, as the members' employers, must make the appropriate amount of contributions based on the amount of worker's compensation that MPSERS had recognized as reportable compensation. We effectively affirm respondent board's findings, however, with respect to worker's compensation payments made to MPSERS members on or after June 12, 1996, pursuant to 1996 P.A. 268. We remand this case to the trial court for entry of an order and further proceedings consistent with this opinion. We do not retain jurisdiction.
Reversed in part, affirmed in part, and remanded.
NOTES
[*]  Circuit judge, sitting on the Court of Appeals by assignment.
