In the Matter of the Child of:  I.S., Parent.

may not be cited except as provided by

Minn. Stat. § 480 A. 08, subd. 3 (1998).

 STATE OF MINNESOTA

 IN COURT OF APPEALS

 C9-99-60

In the Matter of the Application

for the Continuation of Total and

Permanent Disability Benefits for

James M. Hillman.

 Filed August 31, 1999

 Affirmed

 Peterson, Judge

Public Employees Retirement Association

Agency File No. 199086

David J. Hoekstra, Jardine, Logan & O'Brien, P.L.L.P., 2100 Piper Jaffray Plaza, 444 Cedar Street, St. Paul, MN 55101 (for relator)

Mike Hatch, Attorney General, Rory H. Foley, Assistant Attorney General, 525 Park Street, Suite 500, St. Paul, MN 55103-2106 (for respondent)

Considered and decided by Shumaker, Presiding Judge, Short, Judge, and Peterson, Judge.

 U N P U B L I S H E D O P I N I O N

 PETERSON, Judge

Relator James M. Hillman challenges an order of respondent Public Employees Retirement Association (PERA) Board of Trustees denying his application for continued total and permanent disability benefits. We affirm.

 FACTS

Hillman worked for St. Paul Independent School District #625 from 1970 to 1979 and for the St. Paul Department of Planning and Economic Development from 1985 to 1996. While working as a groundskeeper for the school district, Hillman sustained work-related back injuries in 1972, 1973, and 1978.

In September 1996, following back surgery, Hillman applied for total and permanent disability benefits with PERA, claiming he was unable to sit, drive, or concentrate due to lower back pain. Dr. John Lonstein filed a disability report with PERA, which concluded that Hillman had a degenerative disk disease and was totally and permanently disabled. PERA's medical advisor, Dr. William J. Paule, reviewed Hillman's medical records and his application for disability benefits and concluded that under the PERA statute, Hillman was totally and permanently disabled. On February 13, 1997, PERA approved Hillman's application for total and permanent disability benefits.

In January 1998, Hillman began working as a hall greeter for the St. Paul school district. In this position, which is primarily sedentary, Hillman greets and assists people when they come into a school building. Hillman works seven and one-half hours per day, five days a week, earning approximately $10.60 per hour. He also accrues sick leave and vacation time.

Also in January 1998, upon PERA's request, Hillman filed an application to continue total and permanent disability benefits. To support this application, Dr. R. Paul Post filed a disability continuation medical report with PERA. The report stated that Hillman continued to have the same level of chronic back pain and was unable to do repeated lifting, bending, or twisting, and could not sit or stand for longer than 20 minutes at a time. Post concluded that Hillman was totally and permanently disabled under the meaning of the PERA statute. PERA's medical advisor, Dr. Valentine O'Malley, reviewed Hillman's application and medical records and concluded that his disability benefits should be suspended because he was working full time as a hall greeter and, thus, no longer met PERA's criteria for total and permanent disability.

A fact-finding conference was held before an administrative law judge (ALJ) to determine whether Hillman continued to be totally and permanently disabled. The ALJ recommended that although the record demonstrated that Hillman had "a serious, degenerative disk disease affecting his lower back," the PERA board should deny his application for continued disability benefits because he was working full time at a gainful wage and, thus, was able to engage in "substantial gainful activity." The PERA board issued a final order that adopted the ALJ's findings and conclusions and denied Hillman's application for continued disability benefits.

 D E C I S I O N

Review by certiorari is

confined to questions affecting the jurisdiction of the board, the regularity of its proceedings, and, as to the merits of the controversy, whether the order or determination in a particular case was arbitrary, oppressive, unreasonable, fraudulent, under an erroneous theory of law, or without any evidence to support it.

 Dietz v. Dodge County, 487 N.W.2d 237, 239 (Minn. 1992) (quotation omitted); see also In re Quantification of Environmental Costs, 578 N.W.2d 794, 799 (Minn. App. 1998) (when agency acts in quasi-judicial capacity, its factual findings will be affirmed unless unsupported by substantial evidence), review denied (Minn. Aug. 18, 1998).

Decisions of administrative agencies enjoy a presumption of correctness, and reviewing courts should defer to an agency's expertise and special knowledge. Reserve Mining Co. v. Herbst, 256 N.W.2d 808, 824 (Minn. 1977). In addition, although this court is not bound by an agency's construction of a governing statute,

"[w]hen the meaning of a statue is doubtful, courts should give great weight to a construction placed upon it by the department charged with its administration."

 Goodnature v. Mower County, 558 N.W.2d 19, 20 (Minn. App. 1997) (quoting Krumm v. R.A. Nadeau Co., 276 N.W.2d 641, 644 (Minn. 1979)) (alteration in original). A public retirement fund board is analogous to an administrative agency. Axelson v. Minneapolis Teachers' Retirement Fund Ass'n, 544 N.W.2d 297, 299 (Minn. 1996). PERA is a public retirement fund administered by a board of trustees. Minn. Stat. §§ 353.01, .03, .27 (1998).

Members of PERA who have at least three years of service are entitled to receive disability benefits if they become totally and permanently disabled before reaching their normal retirement age. Minn. Stat. § 353.33, subd. 1 (1998). "Total and permanent disability" is defined as

the inability to engage in any substantial gainful activity by reason of any medically determinable physical or mental impairment which can be expected to be of long-continued and indefinite duration. Long-continued and indefinite duration means that the disability has been or is expected to be for a period of at least one year.

Minn. Stat. § 353.01, subd. 19 (1998).

The PERA board determined that because Hillman is employed at a gainful wage on a full-time basis, he is able to engage in substantial gainful activity and, therefore, no longer suffers from a total and permanent disability. Hillman argues that because he had been determined to be eligible to receive disability benefits, the PERA board erred as a matter of law by not applying Minn. Stat. § 353.33, subd. 7 (1998), to determine his eligibility for continued benefits. Minn. Stat. § 353.33, subd. 7, provides:

If, following a work or non-work-related injury or illness, a disabled person resumes a gainful occupation from which earnings are less than the salary at the date of disability or the salary currently paid for similar positions, the board shall continue the disability benefit in an amount that, when added to the earnings and workers' compensation benefit, does not exceed the salary at the date of disability or the salary currently paid for similar positions, whichever is higher, provided the disability benefit does not exceed the disability benefit originally allowed * * *.

Hillman contends that under the plain language of this statute, he is eligible to continue receiving disability benefits in a reduced amount. But we conclude that the language of the statute is ambiguous. See State by Beaulieu v. RSJ, Inc., 552 N.W.2d 695, 701 (Minn. 1996) (statute is ambiguous if it is reasonably susceptible to more than one interpretation). "Gainful occupation," the term used in Minn. Stat. § 353.33, subd. 7, and "substantial gainful activity," the term used in Minn. Stat. § 353.01, subd. 19, are not defined by statute or rule. It is not apparent from the statutory language whether these terms have a single meaning or different meanings.

The PERA board has resolved this ambiguity by concluding that "gainful occupation" means activity less significant than "substantial gainful activity." The PERA board has consistently held that Minn. Stat. § 353.33, subd. 7, does not apply to an applicant who is able to engage in substantial gainful activity because the applicant is no longer considered to be totally and permanently disabled. In contrast, an applicant who is only able to resume a gainful occupation continues to be considered disabled and is eligible to receive a reduced disability benefit. See, e.g., In re Randolph A. Schacht v. PERA, Office of Admin. Hearings No. 1-3600-6269-5 (PERA April 29, 1992); see also In re Application for Disability Benefits of James R. Leighton, Office of Admin. Hearings No. 11-3600-6148-2 (PERA May 11, 19920 (following Schacht).

Because the meanings of "substantial gainful activity" and "gainful occupation" are doubtful, we give great weight to the meanings placed upon these terms by the PERA board. See Goodman v. State, Dep't of Pub. Safety, 282 N.W.2d 559, 560 (Minn. 1979) (reviewing court's practice when faced with ambiguous statute "is to accord substantial consideration to the interpretation of the administrators working daily with the problem sought to be remedied"). We also note that the meanings placed upon these terms by the PERA board permit Minn. Stat. §§ 353.01, subd. 19, 353.33, subd. 7, to be interpreted in a consistent manner that gives meaning to both subdivisions. See Minn. Stat. § 645.17(2) (1998) (legislature intends entire statute to be effective and certain). The PERA board did not err by interpreting the PERA statute as it did.

Hillman also argues that the PERA board's findings, conclusions, and order denying his application for continued disability benefits is arbitrary and capricious and not supported by substantial evidence. We disagree.

An agency decision is arbitrary or capricious when it represents an agency's will rather than its judgment. Mammenga v. State Dep't of Human Servs., 442 N.W.2d 786, 789 (Minn. 1989) (citing Markwardt v. State Water Resources Bd., 254 N.W.2d 371, 374 (Minn. 1977)). Substantial evidence means

(1) such relevant evidence as a reasonable mind might accept as adequate to support a conclusion; (2) more than a scintilla of evidence; (3) more than "some evidence"; (4) more than "any evidence"; and (5) evidence considered in its entirety.

 Reserve Mining, 256 N.W.2d at 825.

In February 1997, when Hillman initially applied for total and permanent disability benefits, he was not working in any capacity. PERA's medical consultant reviewed Hillman's medical records and disability application and concluded that Hillman had a total and permanent disability as defined in the PERA statute. But, in January 1998, Hillman went back to work for the school district as a hall greeter.

When Hillman applied for continued total and permanent disability benefits, PERA's medical consultant reviewed his medical records and disability application, and concluded that in view of Hillman's full-time employment as a hall greeter, his condition no longer fell within the definition of total and permanent disability. In addition, Susan Luce, a qualified rehabilitation consultant, met with Hillman and conducted an employment assessment. In her report, Luce noted that Hillman was employed full time as a hall greeter and concluded that Hillman was "employable and capable of working within his restrictions and attained skills."

Based on this evidence, the PERA board concluded that despite his degenerative disk disease, Hillman was able to engage in substantial gainful activity as a hall greeter and, therefore, was not totally and permanently disabled under Minn. Stat. § 353.01, subd. 19.

Hillman's full-time work activity is more extensive than the work activity of other employees who were initially determined to be disabled but later began working and, as a result, were determined by the PERA board to be ineligible to receive continued disability benefits. See, e.g., Schacht, Office of Admin. Hearings No. 1-3600-6269-5 (applicant unable to work in former employment as a court reporter due to a disability, but working 30 hours per week during nine months of year as a teacher's aide denied continued disability benefits because he was engaged in "substantial gainful activity" for purposes of Minn. Stat. § 353.01, subd. 19).

The PERA board's decision that Hillman did not qualify for continued disability benefits because he was engaged in substantial gainful activity and, therefore, did not have a total and permanent disability within the meaning of Minn. Stat. § 353.01, subd. 19, is supported by substantial evidence, and is not arbitrary and capricious, or affected by an error of law.

  Affirmed.