We granted leave in this case to review a 1993 declaratory ruling of the Michigan Public School Employees Retirement Board. The board concluded that worker’s compensation payments made to an injured employee, who was unable to work between March 13, 1992, and June 12, 1996,1 constitute sick leave pay and thus are reportable compensation. We affirm that ruling.
I. FACTUAL AND PROCEDURAL BACKGROUND
On September 5, 1990, Ms. Bessie Traylor, age fifty-eight, fell and broke her hip while at work. At the time, she was employed by one of the plaintiff school districts and had earned 29.8 years of retirement service credit. She began receiving worker’s compensation payments for her injury and, later, sought regular service retirement benefits from the Michigan Public School Employees Retirement System in lieu of disability benefits. The retirement system advised her that her worker’s compensation payments were not considered “compensation” for purposes of calculating her retirement service credit.
*329As a consequence, Ms. Traylor would have received less than thirty years of service credit, greatly reducing her lifetime retirement benefits. Had she been given credit for the time she collected worker’s compensation payments, she would have retired with 30.8 years’ service and her full retirement package. Ms. Traylor contested the retirement system’s denial of one year of retirement service credit and received an adverse ruling.
She then filed an exception with the Michigan Public School Employees Retirement Board. The board unanimously granted her request. It ordered her account credited for both the compensation and service time lost while she received worker’s compensation benefits, beginning September 6, 1990, the date of her injury.
On March 13, 1992, the retirement board adopted a policy consistent with this decision and, later, notified the school districts.2 The districts sought and received a hearing from the retirement board, which issued a declaratory ruling affirming its policy on July 30, 1993. It stated that employees were to receive retirement credit for the time they received worker’s compensation payments due to an injury incurred in the employment of a member school district.
*330The school districts appealed to the Ingham Circuit Court, which affirmed the declaratory ruling. They next appealed to the Court of Appeals, which reversed the circuit court’s order.3
The Court held that retirement system members were not entitled to retirement service credit for periods during which they received worker’s compensation benefits.4 We granted defendants’ application for leave to appeal.5
H. ANALYSIS
The issue before us is whether the term “compensation” includes worker’s compensation payments received for an injury suffered by a public school employee between March 13, 1992, and June 12, 1996.
A
The definition of “compensation” under consideration in this case appeared at MCL 38.1304(1); MSA 15.893(114)(1):6
“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 *331annuity 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.]
The Court of Appeals determined that the phrase “sick leave pay while absent from work” did not include worker’s compensation payments made to a public school employee injured while at work. To support its conclusion, it cited two statutes that specifically enumerate instances when a member may receive credit for periods worker’s compensation benefits are drawn.7 The Court concluded that, had the Legislature intended that all members receive service credit while drawing worker’s compensation benefits, the statutory exceptions would be rendered nugatory. We disagree.
*332In scrutinizing the declaratory ruling of the retirement board, we keep in mind the limits of judicial review. The Michigan Constitution provides that review of matters, including declaratory rulings, “shall include, as a minimum, the determination whether such final decisions, findings, rulings and orders are authorized by law . . . .” Const 1963, art 6, § 28.
We will set aside the legal rulings of administrative agencies if they violate the constitution or a statute or contain a substantial and material error of law. MCL 24.306(l)(a), (f); MSA 3.560(206)(l)(a), (f); Amalgamated Transit Union, Local 1564, AFL-CIO v Southeastern Michigan Transportation Authority, 437 Mich 441, 450; 473 NW2d 249 (1991). Declaratory rulings are subject to the same judicial review as an agency’s final decision or order in a contested case. MCL 24.263; MSA 3.560(163). We give them deference, provided they are consistent with the purpose and policies of the statute in question. Empire Iron Mining Partnership v Orhanen, 455 Mich 410, 416; 565 NW2d 844 (1997).
In reviewing statutes, our primary goal is to ascertain and give effect to the intent of the Legislature. Farrington v Total Petroleum, Inc, 442 Mich 201, 212; 501 NW2d 76 (1993). If a statute’s wording is certain and unambiguous, we do not interpret it. Turner v Auto Club Ins Ass’n, 448 Mich 22, 27; 528 NW2d 681 (1995). However, if reasonable minds can differ regarding its meaning, then judicial construction is appropriate. Yaldo v North Pointe Ins Co, 457 Mich 341; 578 NW2d 274 (1998). In this case, we find that reasonable minds can differ regarding the statutory meaning of “compensation.” Therefore, judicial construction is appropriate.
*333The question presented here is whether the retirement board wrongly extended the law. The board concluded that worker’s compensation benefits are functionally the same as sick leave pay. It reasoned that the benefits are no less remuneration than is sick leave paid while the employee is absent from work. We agree. We find that the retirement board made a faithful reading of the Legislature’s intent when it interpreted the statutory language.
As this Court stated in McAvoy v H B Sherman Co, 401 Mich 419, 437; 258 NW2d 414 (1977):
The objective of the social legislation [worker’s disability compensation legislation] is to provide the disabled worker with benefits during the period of his disability so that the worker and his dependents may survive (literally) the catastrophe which the temporary cessation of necessary income occasions. [Emphasis deleted.]
To the extent that worker’s disability compensation benefits are intended to replace wages, they are a form of remuneration.
The United States Supreme Court has articulated the public policy objective underlying the furnishing of retirement benefits. It is to provide assistance to aged individuals who, having rendered long and valuable employment service, are no longer able to labor productively. Helvering v Davis, 301 US 619; 57 S Ct 904; 81 L Ed 1307 (1937). The retirement board’s interpretation of the retirement act clearly supports the policy of providing financial security to public school employees who qualify for retirement.
The Legislature’s use of the term “compensation” in the retirement act suggests that a broad interpretation is appropriate in crediting remuneration received by *334public school employees. The Legislature could have chosen words having a nonrestrictive meaning. It could have selected the word “salary” as the basis for retirement credit. “Salary” has been defined as a periodic payment made to a person for official or professional services or for regular work. See People v Lay, 193 Mich 476, 488; 160 NW 467 (1916).
In this case, the plaintiff school districts argued, and the Court of Appeals agreed, that the appropriate rule of statutory construction is expressio unius est exclusio alterius.8 They point out that worker’s disability compensation benefits were not expressly listed as a form of “compensation” in subsection 4(1) of the retirement act. Therefore, they urge that the Legislature must have intended to exclude them from being treated as creditable compensation under the act.
This inteipretation is inappropriate for two reasons. First, included in the items comprising “compensation” is “sick leave pay while absent from work.” Worker’s disability compensation benefits are a form of sick leave pay because they are compensation for illness or injury suffered by a public school employee while on the job. Accordingly, a reasonable inteipretation of “sick leave pay” encompasses worker’s disability compensation benefits.
Second, subsection 4(1) specifically identifies what types of remuneration are not included in the definition of compensation under the retirement act:
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 *335school employees, and remuneration paid for the specific purpose of increasing the final average compensation. [MCL 38.1304(1); MSA 15.893(114)(1).]
Worker’s disability compensation is not an expressly excluded form of remuneration. Hence, it must be viewed as falling within the expansive definition of compensation. Common sense dictates that it must be included in the phrase “sick leave pay while absent from work.” The Legislature provided a list of inclusive phrases to outline types of remuneration included in the term “compensation,” such as the phrase “sick leave pay while absent from work.” It seems likely that it chose that terminology because, had it done otherwise, the retirement act would have to be amended each time a new form of compensation is negotiated.
The retirement board’s interpretation of the retirement act is supported, also, by legislative history. In 1980, the chapters dividing school districts into two separate classes were consolidated. The consolidation provided benefits to all school districts that earlier had been available only to school employees in the Detroit public schools. A legislative analysis of Senate Bill 104, which became 1980 PA 300, provided the following:
Outstate members would also gain the right to count time spent on sabbatical leave and time receiving worker’s compensation as service credit. Both these benefits are now enjoyed by Detroit members. [Senate Legislative Analysis, SB 104, September 23, 1980.]
Thus, in making its declaratory ruling that disability payments are a form of sick leave pay that earn *336retirement service credit, the retirement board gave effect to the Legislature’s intent.9
In 1986, the retirement system issued a memorandum stating that worker’s compensation benefits do not qualify as reportable compensation for retirement purposes. The school districts claim that the retirement board suddenly reversed its policy with its decision in Traylor v MPSERS. However, it must be noted that the 1986 memorandum provided the retirement system’s interpretation of sick leave pay, not the retirement board’s position. The retirement board governs and administers the retirement system, subject to the provisions of the retirement act. The retirement board’s interpretation of “compensation” and resulting decision in Traylor superseded the retirement system staff’s interpretation. Traylor provided the retirement board with its first opportunity to address this issue.
The public policy that allows agencies to establish new principles through contested case proceedings is premised on the fact that an agency cannot promulgate rules to cover every conceivable situation. The agency must interpret the statute it administers, and its interpretations are entitled to great weight. Magreta v Ambassador Steel Co, 380 Mich 513; 158 NW2d 473 (1968).
*337B
While this case was pending in the Court of Appeals, the Legislature amended the definition of “compensation” to expressly include the retirement board’s interpretation. It defined the term “compensation” as
salary and wages and all of- the following:
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.1101
The Court of Appeals opinion in this case maintained that the Legislature’s action actually supported the school districts’ position. On the contrary, the action of the Legislature in amending the definition of “compensation” must be interpreted as a ratification of the position of the retirement board. We have long and repeatedly held that, when a legislative amendment is enacted soon after a controversy arises regarding the meaning of an act, “ ‘ “it is logical to regard the amendment as a legislative interpretation of the original act . . . ” Detroit v Walker, 445 Mich 682, 697; 520 NW2d 135 (1994), quoting Detroit Edison Co v Dep’t of Revenue, 320 Mich 506, 520; 31 NW2d 809 (1948), quoting 1 Sutherland, Statutory Construction (3d ed), § 1931, p 418. In this case, the Legislature’s amendment of the retirement act clarifies its consistent intent.
*338Therefore, we find that the retirement board properly applied the statute when it issued its declaratory ruling.11 Worker’s compensation payments made between March 13, 1992, and June 12, 1996, are compensation, and retirement service credit should be granted for them.
m. CONCLUSION
We reverse that portion of the Court of Appeals decision that reversed part of the declaratory ruling of the Michigan Public School Employees Retirement Board. We hold that weekly worker’s compensation payments made between March 13, 1992, and June 12, 1996, are sick leave pay for retirement purposes.
Mallett, C.J., and Cavanagh and Boyle, JJ., concurred with Kelly, J.This time frame represents the period between the implementation of the Michigan Public School Employees Retirement Board decision in Traylor v MPSERS, and the effective date of 1996 PA 268.
A memorandum dated September 25, 1992, from Barbara Grover of the Michigan Public School Employees Retirement System advised member reporting units that
[t]he Michigan Public School Employees Retirement Board has acted to recognize Weekly Worker’s Compensation payments as sick leave pay while absent from work and grant retirement credit for the time a member is receiving Weekly Worker’s Compensation. Previously, school employees were not granted credit while receiving these payments.
The Court affirmed the retirement board’s findings with respect to worker’s compensation payments made to retirement system members on or after June 12, 1996, pursuant to 1996 PA 268. It also found that a declaratory ruling by a state board is not a rule for the purpose of the rule-making requirements of the Administrative Procedures Act. These issues are not before this Court.
219 Mich App 456; 556 NW2d 524 (1996).
456 Mich 920 (1998).
Amended by 1996 PA 268, MCL 38.1303a; MSA 15.893(113a).
A member totally and permanently disabled by a work-related injury may receive service credit for the time worker’s compensation benefits are paid if the member recovers and returns to work. MCL 38.1387; MSA 15.893(197). Also, 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. It is computed as if the deceased member had retired on the day preceding the date of the member’s death. MCL 38.1390; MSA 15.893(200).
The expression of one thing is the exclusion of all others.
We disagree with the assertion in the dissent that we are relying on legislative history as authority to abrogate the clear language of a statute. Rather, we provide the legislative analysis to demonstrate the retirement board’s proper interpretation of the Legislature’s intent to provide service credit for time spent receiving worker’s compensation.
Subsection 3a(2)(f) of 1996 PA 268, MCL 38.1303a; MSA 15.893(113a).
The dissent is misguided in its representation that we are giving the 1996 amendment by the Legislature retroactive effect. The dissent has lost sight of the issue in this case, which is whether the retirement board wrongly extended the law when it made its 1993 declaratory ruling. Our holding is that the board properly applied the statute in its declaratory ruling, thus affirming its determination that retirement service credit should be granted for the period March 13, 1992, to June 12, 1996. We do not give the 1996 amendment retroactive effect. Rather, we give effect to the retirement board’s 1993 declaratory ruling.