Rapoza, CJ.
The plaintiff, William Hunter, Sr., appeals from a judgment entered in the Superior Court in favor of the Contributory Retirement Appeal Board (CRAB), which determined that Hunter was correctly classified for retirement purposes pursuant to G. L. c. 32, § 3(2)(g), as a Group 2 employee. On [258]*258appeal, Hunter argues that CRAB should have classified him in Group 4 because he regularly performed duties of a correction officer and the term “correction officerQ” is explicitly included in the statute relating to Group 4 membership. He also argues that because the Essex County retirement board (county board) at one point classified him in Group 4, the State Board of Retirement (State board) was precluded by G. L. c. 34B, § 14(a), from reclassifying him in Group 2. For the reasons discussed below, we discern no error and affirm.
Facts. On September 30, 2003, Hunter, an employee of the Essex County sheriff’s department (department), retired under the department’s early retirement incentive program. The State board classified him, based on his position as “Maintenance Personnel,” in Group 2 for retirement purposes. He retired without appealing the State board’s decision even though the county board had previously classified him, prior to the State takeover of the Essex County retirement system, as being in Group 4. Not until December 26, 2006, did Hunter write to the State board to request a change in his classification to Group 4. The State board determined that Hunter was correctly classified in Group 2 based on its interpretation of G. L. c. 32, § 3(2)(g), and Hunter appealed to the Division of Administrative Law Appeals (DALA). After a hearing, an administrative magistrate for DALA concluded that Hunter was properly classified in Group 2.
The administrative magistrate found the following facts, all of which CRAB subsequently incorporated by reference into its decision. Hunter joined the Essex County retirement system in 1996, and at that time listed his title as “janitor.” On May 9, 1997, he requested that the county board reclassify him from Group 2 to Group 4 on the grounds that his duties involved working with and supervising inmates. The department supported Hunter’s request, stating that “[sjince part of his duty is supervising inmates ... we feel that he should be reclassified to Group 4.” The county board granted the request.
In 1999, Essex County government was abolished and its employees, including Hunter, were transferred to the State retirement system. On August 14, 2003, on a group classification questionnaire, Hunter listed his job title and employing agency as “Tool Room Attendant/Janitor/Essex County Sheriff’s Department.” Thereafter, the State board classified him in Group 2.
[259]*259Hunter’s job description included a provision stating that he “[m]ust be able to supervise and direct inmates.” The first responsibility in his job description was to “[djirectly supervise inmates on a shift, assuring that they complete their assignments and provide [unjinterrupted services for the facility.” The administrative magistrate for DALA also found “[t]he petitioner wore a uniform to work every day and he was given a number of keys with which to navigate his way about the facility and lead inmates to job assignments. He also took inmates outside of the facility to maintain the grounds.”
The administrative magistrate concluded, based on Gaw v. Contributory Retirement Appeal Bd., 4 Mass. App. Ct. 250, 254 (1976), that Hunter did not qualify for Group 4 because his position as “Tool Room Attendant” does not appear among the job titles listed in Group 4. Rather, according to the administrative magistrate, Hunter was correctly classified in Group 2 under the category of employees “whose regular and major duties require them to have the care, custody, instruction or other supervision of prisoners.”
Hunter subsequently appealed to CRAB, which affirmed the decision of the administrative magistrate “for the reasons stated in the DALA magistrate’s [cjonclusion.” Pursuant to G. L. c. 30A, § 14, Hunter appealed to the Superior Court, which affirmed the decision of CRAB.
Discussion. 1. Standard of review. Judicial review under G. L. c. 30A, § 14, is limited to determining whether the agency’s decision was unsupported by substantial evidence, arbitrary and capricious, or otherwise based on an error of law. See Retirement Bd. of Brookline v. Contributory Retirement Appeal Bd., 33 Mass. App. Ct. 478, 480 (1992); Flanagan v. Contributory Retirement Appeal Bd., 51 Mass. App. Ct. 862, 864 (2001). In reviewing a CRAB decision, courts must “give due weight to the experience, technical competence, and specialized knowledge of the agency, as well as to the discretionary authority conferred upon it.” Dube v. Contributory Retirement Appeal Bd., 50 Mass. App. Ct. 21, 23 (2000), quoting from G. L. c. 30A, § 14(7). See Rockett v. State Bd. of Retirement, 77 Mass. App. Ct. 434, 438 (2010).
On appeal, we review whether a CRAB decision was unsup[260]*260ported by substantial evidence; however, we review CRAB’s legal conclusions de novo and give no special weight to the Superior Court’s decision. See Flanagan, supra at 864; Damiano v. Contributory Retirement Appeal Bd., 72 Mass. App. Ct. 259, 261 (2008). Although we are thus charged with the duty of statutory interpretation, “[w]here an agency’s interpretation of a statute is reasonable, the court should not supplant it with its own judgment.” Boston Retirement Bd. v. Contributory Retirement Appeal Bd., 441 Mass. 78, 82 (2004), quoting from Flemings v. Contributory Retirement Appeal Bd., 431 Mass. 374, 375 (2000).
2. Classification pursuant to G. L. c. 32, § 3(2)(g). The applicable portion of G. L. c. 32, § 3(2)(g), amended by St. 1979, c. 485, § 1, defines Group 2 members as “employees of the commonwealth or of any county, regardless of any official classification, except the sheriff, superintendent, deputy superintendent, assistant deputy superintendent and correction officers of county correctional facilities, whose regular and major duties require them to have the care, custody, instruction or other supervision of prisoners.” Group 4 membership, in turn, includes “the sheriff, superintendent, assistant superintendent, assistant deputy superintendent and correction officers of county correctional facilities.” G. L. c. 32, § 3(2)(g), amended by St. 1979, c. 485, § 2.
We have not had prior occasion to determine whether an employee who performs duties of a correction officer, but does not have that job title, should be classified in Group 2 or Group 4. In the circumstances presented, however, we see no reason to depart from our analysis in Gaw, supra at 254. In that case, we reviewed G. L. c. 32, § 3(2)(g), to determine whether an employee of a municipal electric power plant should have been classified in Group 1 or Group 4.2 Ibid. We concluded that the statute classifies employees in “Group 4 by naming their posi[261]*261tions or titles rather than ... the type of work they perform.” Ibid.
The same is true for classification in Group 2, with two exceptions, one of which is relevant here. Ibid.
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Rapoza, CJ.
The plaintiff, William Hunter, Sr., appeals from a judgment entered in the Superior Court in favor of the Contributory Retirement Appeal Board (CRAB), which determined that Hunter was correctly classified for retirement purposes pursuant to G. L. c. 32, § 3(2)(g), as a Group 2 employee. On [258]*258appeal, Hunter argues that CRAB should have classified him in Group 4 because he regularly performed duties of a correction officer and the term “correction officerQ” is explicitly included in the statute relating to Group 4 membership. He also argues that because the Essex County retirement board (county board) at one point classified him in Group 4, the State Board of Retirement (State board) was precluded by G. L. c. 34B, § 14(a), from reclassifying him in Group 2. For the reasons discussed below, we discern no error and affirm.
Facts. On September 30, 2003, Hunter, an employee of the Essex County sheriff’s department (department), retired under the department’s early retirement incentive program. The State board classified him, based on his position as “Maintenance Personnel,” in Group 2 for retirement purposes. He retired without appealing the State board’s decision even though the county board had previously classified him, prior to the State takeover of the Essex County retirement system, as being in Group 4. Not until December 26, 2006, did Hunter write to the State board to request a change in his classification to Group 4. The State board determined that Hunter was correctly classified in Group 2 based on its interpretation of G. L. c. 32, § 3(2)(g), and Hunter appealed to the Division of Administrative Law Appeals (DALA). After a hearing, an administrative magistrate for DALA concluded that Hunter was properly classified in Group 2.
The administrative magistrate found the following facts, all of which CRAB subsequently incorporated by reference into its decision. Hunter joined the Essex County retirement system in 1996, and at that time listed his title as “janitor.” On May 9, 1997, he requested that the county board reclassify him from Group 2 to Group 4 on the grounds that his duties involved working with and supervising inmates. The department supported Hunter’s request, stating that “[sjince part of his duty is supervising inmates ... we feel that he should be reclassified to Group 4.” The county board granted the request.
In 1999, Essex County government was abolished and its employees, including Hunter, were transferred to the State retirement system. On August 14, 2003, on a group classification questionnaire, Hunter listed his job title and employing agency as “Tool Room Attendant/Janitor/Essex County Sheriff’s Department.” Thereafter, the State board classified him in Group 2.
[259]*259Hunter’s job description included a provision stating that he “[m]ust be able to supervise and direct inmates.” The first responsibility in his job description was to “[djirectly supervise inmates on a shift, assuring that they complete their assignments and provide [unjinterrupted services for the facility.” The administrative magistrate for DALA also found “[t]he petitioner wore a uniform to work every day and he was given a number of keys with which to navigate his way about the facility and lead inmates to job assignments. He also took inmates outside of the facility to maintain the grounds.”
The administrative magistrate concluded, based on Gaw v. Contributory Retirement Appeal Bd., 4 Mass. App. Ct. 250, 254 (1976), that Hunter did not qualify for Group 4 because his position as “Tool Room Attendant” does not appear among the job titles listed in Group 4. Rather, according to the administrative magistrate, Hunter was correctly classified in Group 2 under the category of employees “whose regular and major duties require them to have the care, custody, instruction or other supervision of prisoners.”
Hunter subsequently appealed to CRAB, which affirmed the decision of the administrative magistrate “for the reasons stated in the DALA magistrate’s [cjonclusion.” Pursuant to G. L. c. 30A, § 14, Hunter appealed to the Superior Court, which affirmed the decision of CRAB.
Discussion. 1. Standard of review. Judicial review under G. L. c. 30A, § 14, is limited to determining whether the agency’s decision was unsupported by substantial evidence, arbitrary and capricious, or otherwise based on an error of law. See Retirement Bd. of Brookline v. Contributory Retirement Appeal Bd., 33 Mass. App. Ct. 478, 480 (1992); Flanagan v. Contributory Retirement Appeal Bd., 51 Mass. App. Ct. 862, 864 (2001). In reviewing a CRAB decision, courts must “give due weight to the experience, technical competence, and specialized knowledge of the agency, as well as to the discretionary authority conferred upon it.” Dube v. Contributory Retirement Appeal Bd., 50 Mass. App. Ct. 21, 23 (2000), quoting from G. L. c. 30A, § 14(7). See Rockett v. State Bd. of Retirement, 77 Mass. App. Ct. 434, 438 (2010).
On appeal, we review whether a CRAB decision was unsup[260]*260ported by substantial evidence; however, we review CRAB’s legal conclusions de novo and give no special weight to the Superior Court’s decision. See Flanagan, supra at 864; Damiano v. Contributory Retirement Appeal Bd., 72 Mass. App. Ct. 259, 261 (2008). Although we are thus charged with the duty of statutory interpretation, “[w]here an agency’s interpretation of a statute is reasonable, the court should not supplant it with its own judgment.” Boston Retirement Bd. v. Contributory Retirement Appeal Bd., 441 Mass. 78, 82 (2004), quoting from Flemings v. Contributory Retirement Appeal Bd., 431 Mass. 374, 375 (2000).
2. Classification pursuant to G. L. c. 32, § 3(2)(g). The applicable portion of G. L. c. 32, § 3(2)(g), amended by St. 1979, c. 485, § 1, defines Group 2 members as “employees of the commonwealth or of any county, regardless of any official classification, except the sheriff, superintendent, deputy superintendent, assistant deputy superintendent and correction officers of county correctional facilities, whose regular and major duties require them to have the care, custody, instruction or other supervision of prisoners.” Group 4 membership, in turn, includes “the sheriff, superintendent, assistant superintendent, assistant deputy superintendent and correction officers of county correctional facilities.” G. L. c. 32, § 3(2)(g), amended by St. 1979, c. 485, § 2.
We have not had prior occasion to determine whether an employee who performs duties of a correction officer, but does not have that job title, should be classified in Group 2 or Group 4. In the circumstances presented, however, we see no reason to depart from our analysis in Gaw, supra at 254. In that case, we reviewed G. L. c. 32, § 3(2)(g), to determine whether an employee of a municipal electric power plant should have been classified in Group 1 or Group 4.2 Ibid. We concluded that the statute classifies employees in “Group 4 by naming their posi[261]*261tions or titles rather than ... the type of work they perform.” Ibid.
The same is true for classification in Group 2, with two exceptions, one of which is relevant here. Ibid. Group 2 specifically excludes, by job title, “the sheriff, superintendent, deputy superintendent, assistant deputy superintendent and correction officers of county correctional facilities,” while including all other “employees of the commonwealth or of any county, regardless of any official classification, . . . whose regular and major duties require them to have the care, custody, instruction or other supervision of prisoners.” G. L. c. 32, § 3(2)(g). See Gaw, supra at 254-255. Consequently, an employee other than a correction officer, whose regular and major duties involve such activities with regard to prisoners, is properly included in Group 2. See ibid. The statute thus recognizes two groups of employees who have duties pertaining to prisoners: those who by job title, including correction officers, are classified in Group 4, and all other employees with such responsibilities who are classified in Group 2.
Here, GRAB’S interpretation of the statute was reasonable and in accordance with the law. See Boston Retirement Bd., supra at 82. Furthermore, the decision of CRAB to classify Hunter in Group 2 was supported by substantial evidence and was not arbitrary and capricious. In denying Hunter’s request for a change in group membership, CRAB observed that Hunter listed his job title as “Tool Room Attendant/!anitor ’’ in his group classification questionnaire, and that the director of human resources for the Essex County correctional facility stated in a 1997 letter to the county board that Hunter’s position was “Tool Room Attendant.” Although CRAB recognized that Hunter’s job description included the direct supervision of inmates, this responsibility did not entitle him to be considered a correction officer for purposes of Group 4 membership. CRAB correctly determined that because none of Hunter’s job titles was specifically named in Group 4, Hunter was not entitled to classification in that group. See Gaw, supra at 254-255.
Hunter relies on Maddocks v. Contributory Retirement Appeal Bd., 369 Mass. 488 (1976), in claiming entitlement to Group 4 membership. Maddocks involved an appeal for reclassification [262]*262from Group 1 to Group 2. The Supreme Judicial Court held that the statutory language used to classify Group 2 membership clearly contemplates a consideration of an employee’s “regular and major” duties in addition to his or her job title if the employee is a county or Commonwealth employee whose regular and major duties require the performance of certain tasks of a hazardous nature. Id. at 493-494. As we recognized in Gaw, supra at 254-255, this clause is an exception to the Legislature’s general pattern of determining membership based on job title or position. Here, CRAB classified Hunter in Group 2 based on his regular and major duties in accordance with Maddocks. Nothing in Mad-docks, however, would suggest that we extend this analysis to the specific language in Group 4.
Hunter’s reliance on Tabroff v. Contributory Retirement Appeal Bd., 69 Mass. App. Ct. 131, 135 (2007), is also misplaced. In that case we had to determine if an employee with the job title “Supervising Electrical Engineer” qualified for Group 4 retirement status even though that job title does not appear in Group 4.3 To make that determination, we looked to the statute, which includes as members of Group 4 those “employed as . . . supervisors” of municipal linemen. G. L. c. 32, § 3(2)(g), as amended, St. 1993, c. 139. Having done so, we concluded that membership in Group 4 requires the supervision of linemen, but not simply as an incidental aspect of one’s duties. Tabroff, supra at 135. Rather, we determined that Group 4 membership requires that an employee be specifically “employed as a supervisor” of municipal linemen, as was the case with Tabroff, who was a “Supervising Electrical Engineer” hired to perform that particular function. Id. at 132, 135.
The critical distinction between Tabroff and the present case is that in Tabroff, the employee’s job title and corresponding duties specifically qualified him for Group 4 membership. Id. at 135. By contrast, Hunter asks us to ignore his job title, then look at functions he performed and, on that basis, treat him as [263]*263constructively having a job title (correction officer) that would make him eligible for Group 4. What he urges is inconsistent with the statute and our reasoning in Tabroff. See Commonwealth v. Hamilton, 459 Mass. 422, 436 (2011), quoting from Commonwealth v. Woods Hole, Martha’s Vineyard & Nantucket S.S. Authy., 352 Mass. 617, 618 (1967) (“None of the words of a statute is to be regarded as superfluous”). Moreover, it is inconsistent with a plain reading of the definition of Group 2, which recognizes that there are employees “whose regular and major duties require them to have care, custody, instruction or other supervision of prisoners” without being considered a “correction officer” within the meaning of Group 4. G. L. c. 32, § 3(2)(g).
3. Effect of G. L. c. 34B, § 14, on Hunter’s classification. Hunter argues that once the county board classified him in Group 4, even if it were error to do so, G. L. c. 34B, § 14(a), prohibited the State board from later changing his classification.4 We disagree. We see no reason why CRAB cannot correct an erroneous classification. See, e.g., G. L. c. 32, § 20(5)(c)(2), amended by St. 2000, c. 159, § 91 (providing that “[wjhen an error exists in the records maintained by the system or an error is made in computing a benefit ... the records or error shall be corrected and as far as practicable”). See also Hollstein v. Contributory Retirement Appeal Bd., 47 Mass. App. Ct. 109, 110-112 (1999) (discussing authority of Boston retirement board to correct errors in retirement calculations).
Judgment affirmed.