delivered the opinion of the court:
Defendant Odie Washington (Washington), Director, Illinois Department of Corrections (IDOC), appeals from the circuit court’s orders granting plaintiff Noah Braver’s petition for “writ” of mandamus 1 seeking an award of meritorious good-time credits by Washington sufficient to result in Braver’s immediate release from prison, and denying Washington’s motion to vacate the granting order.
Washington raises the issue of whether the circuit court’s decision to grant Braver’s application for mandamus, requiring his immediate release from IDOC custody, was against the manifest weight of the evidence or, alternatively, constituted an abuse of discretion.
On November 10, 1997, Braver filed a combined action for habeas corpus and mandamus against Washington, as Director, claiming that he was being held in custody illegally at an IDOC facility in Vandalia, Illinois, which imprisonment violated his rights to due process and equal protection under the United States and Illinois Constitutions.
The following facts are derived from Braver’s pleadings. On March 19, 1997, Chicago police officers stopped him for a traffic violation while he was driving his car. The officers found a gun in his car and arrested and charged him with the offense of unlawful use of weapons, a Class 4 felony. Braver, an 18-year-old, was unemployed and indigent at the time of his arrest and was unable to make bail, remaining in the custody of the Cook County Department of Corrections (CCDC) during the entire pendency of his case prior to trial.
On August 25, 1997, Braver pled guilty to the offense of unlawful use of weapons. The circuit court entered judgment on his guilty plea and later sentenced him to a term of 18 months in an IDOC facility, ordering that the jail time Braver served in the CCDC (217 days from the date of his arrest to the date of sentencing) be applied to his sentence. On October 24, 1997 (three days after sentencing), Braver *182was transferred from the CCDC to IDOC. When Braver arrived on that date, he had been in custody for 220 days. Although he had already served 220 days of his jail sentence, Braver was not immediately released from IDOC’s custody. Given a projected release date of December 19, 1997, Braver was required by IDOC to serve a total of 276 days in jail, which was in excess of his 270-day sentence (statutory nine-month requirement).
Braver asserted that because of the extreme overcrowding of inmates, IDOC has established a policy of awarding each inmate 90 days of extra meritorious good-time credit, in addition to the statutory day for day “good-time” credit given to each inmate. As a prerequisite to the award of meritorious good-conduct credit, however, IDOC also has a regular policy and custom of requiring each inmate to serve at least 61 days in IDOC or as close to 61 days as the inmate’s sentence will allow.
Braver claimed that IDOC has established a policy whereby its Director has surrendered his discretion, which has been supplemented by an established and regular policy of granting of 90 days meritorious good-time credit to certain classes of inmates, namely, “all inmates who receive the usual and ordinary day for day meritorious good time credit.” Braver claimed to have been a member of the class of inmates who regularly and routinely receives an extra 90 days of meritorious good-time credit and, therefore, should have been released by IDOC immediately upon being placed in its custody. Because his release date was December 19, 1997, he “will serve 94 days in jail in excess of actually serving 6 months in jail,” without any. rational basis for him to be denied “the usual 90 days meritorious good time awarded to all inmates.” If he had had sufficient funds to post bail, he would have been released after serving only 180 days in jail, as opposed to the 276 days he would actually serve, because he would have been given the 90 days of meritorious good-time credit. Accordingly, this IDOC policy violated Braver’s right to equal protection of the law and due process. Relying on Hampton v. Rowe, 88 Ill. App. 3d 352, 410 N.E.2d 511 (1980), and Freeman v. Lane, 129 Ill. App. 3d 1061, 473 N.E.2d 584 (1985), Braver seeks to be treated similarly to an individual able to post bond and receive the automatic 90 days of meritorious good-time awarded to all inmates.
In conclusion, Braver argued that IDOC’s policy of requiring each inmate to serve at least 61 days in IDOC, or as close to 61 days as the sentence will allow, regardless of the amount of jail time the inmate has spent in a county jail, violates an inmate’s rights to equal protection and due process, and prayed that (1) habeas corpus be ordered releasing him from custody immediately, ór, in the alternative, (2) *183 mandamus be ordered, with directions to respondent to treat Braver’s 220 days served in county jail as 220 days served in the penitentiary; and (3) he be granted the 90 days of meritorious good time awarded to all inmates in his classification.
On December 4, 1997, an evidentiary hearing was held on Braver’s combined action. The State called two IDOC employees as witnesses, Mark McHugh and Laurie Schellinger. McHugh testified that the award of meritorious good time is discretionary, explaining that the Director considers the recommendation of staff members at the institution where the person is incarcerated. Such recommendation is made after the inmate has been in the facility for 30 days. Actual awards are not made until the inmate has been in an IDOC facility for 60 days, regardless of whether the inmate has spent time in the county jail prior to the trial or has been out on bond. This time period allows staff to assess the inmate’s adjustment to the system and to determine whether the inmate has earned the award.
McHugh stated that “certainly by no means” is the award given to every inmate. There is no IDOC policy which mandates that every inmate be given the meritorious good-time award. For example, in the fiscal year ending June 30, 1997, 20% of the inmates received less than 90 days, and 13% received no credit. McHugh also explained that there are no written criteria used to determine whether an inmate should be given the award. The factors considered include length of sentence, behavior, nature of the sentence, criminal background and nature of the offense.
Schellinger, IDOC’s legal counsel, testified that one of the reasons for waiting before any meritorious good time is awarded is to enable the staff to have time to observe the inmate and obtain any relevant and available information regarding that individual.
In arriving at its decision, the circuit court recognized the discretionary nature of the award of meritorious good time, but found it was “fundamentally unfair” for Braver, who was unable to make bond, to spend more time in custody than someone who is able to make bond. On December 4, 1997, the court ordered IDOC to release Braver immediately.
On December 8, 1997, Washington filed an emergency motion to ' vacate the court’s December 4, 1997, order, noting that Braver’s action for mandamus was not properly served and, in any event, that it should not have been granted because the award of meritorious good time is a discretionary matter not subject to mandamus. Attached to the motion was the affidavit of Susan O’Leary, IDOC’s chief legal counsel, who averred that the decision to award meritorious good time is made on a case-by-case basis after review by both the institution *184and central office personnel. Meritorious good time is not awarded on a fixed increment of time and can range anywhere from 1 to 90 days.
Washington’s motion included further the affidavit of David M. Boots, IDOC’s planning and research unit manager, whose responsibilities include compiling, analyzing, and generating statistics regarding inmates incarcerated with IDOC. Boots stated that during fiscal year 1997, 18.5% of the inmates released from IDOC facilities received less than 90 days of meritorious good time and 12.9% of those eligible received no meritorious good time.
The motion to vacate also was supported by the affidavit of Diane Jockisch, IDOC’s transfer coordinator, whose staff reviews recommendations for awards of meritorious good time. Jockisch averred that, according to IDOC policy, the review may occur no earlier than 30 days after an inmate is placed in IDOC’s custody, allowing the institution time to observe the inmate’s adjustment to prison and taking into consideration the fact that IDOC rarely receives documentation of an inmate’s pre-IDOC behavior or adjustment. The Director’s decision whether to award meritorious good time generally begins at the institutional level, where a staff recommendation to award meritorious good time is reviewed by the warden of the facility. If the warden approves the recommendation, the transfer coordinator’s office must then approve or deny the recommendation, as designee of the Director. Individual cases are evaluated based on factors including the nature of the inmate’s offense, the inmate’s criminal history and institutional adjustment, and the potential impact of the inmate’s early release on the community.
Jockisch stated that IDOC officials must have time to observe and evaluate an inmate for meritorious-good-time-award consideration and ensure that early inmate releases that may result from such awards do not impact adversely on public safety and security. It is IDOC’s policy that an inmate must serve a minimum of 60 days in its custody prior to being given meritorious good-time credit. She also stated that consideration may be given to whether an inmate is the subject of pending good-conduct-revocation proceedings or other disciplinary matters. Because the State’s 102 counties do not follow the IDOC’s procedures and disciplinary practices, the automatic award of meritorious good time to inmates immediately upon their entry to IDOC custody would result in the unequal treatment of inmates.
On December 9, 1997, the circuit court denied Washington’s motion to vacate, and this appeal followed.
Notwithstanding the fact that defendant sought an order of habeas corpus in his pleadings, as above noted, that remedy was not pursued in the circuit court nor is it argued in this appeal.
*185Further noted is the fact that defendant has served all the prescribed time, thereby rendering this cause moot under ordinary circumstances, unless the matter falls under the “substantial public interest exception.” The criteria for application of the public interest exception include (1) the existence of a question of public nature; (2) the desirability of an authoritive determination for the purpose of guiding public officers in the performance of their duties; and (3) the likelihood that the question will recur. In re A Minor, 127 Ill. 2d 247, 257, 537 N.E.2d 292 (1989); Duncan Publishing, Inc. v. City of Chicago, 304 IIll. App. 3d 778, 783, 709 N.E.2d 1281 (1999). There must be a clear showing of each factor in order to bring a case within this exception. Mount Carmel High School v. Illinois High School Ass’n, 279 Ill. App. 3d 122, 125-26, 664 N.E.2d 252 (1996). This exception is invoked only on rare occasions where there is an extraordinary degree of public concern and interest. People ex rel. Partee v. Murphy, 133 Ill. 2d 402, 410, 550 N.E.2d 998 (1990). The case sub judice presents such circumstances, in that the liberty interests of many hundreds of prisoners may be involved at present, as well as in the future.
I
Washington contends that the circuit court erred in granting Braver’s action for mandamus, requiring his release from IDOC custody, because Braver had no clear right to meritorious good-time credits. Although reviewing courts may differ as to the appropriate standard of review to employ, Washington asserts, the court’s order granting the petition should be reversed because it was against the manifest weight of the evidence or, alternatively, constituted an abuse of the court’s discretion.
Mandamus, an extraordinary remedy, is awarded in the exercise of judicial discretion according to legal principles (People ex rel. Kula v. O’Connell, 394 Ill. 409, 414, 68 N.E.2d 758 (1946); Baldacchino v. Thompson, 289 Ill. App. 3d 104, 109, 682 N.E.2d 182 (1997) (Baldacchino))-, it is appropriate when necessary to compel a public officer to perform purely ministerial duties, requiring no exercise of judgment on the part of the public officer. People ex rel. Pyrzynski v. Daley, 34 Ill. App. 3d 1077, 1080, 341 N.E.2d 24 (1975); Baldacchino, 289 Ill. App. 3d at 109. Mandamus will not issue to direct the manner of performance of an action requiring the exercise of discretion (Freeman v. Lane, 129 Ill. App. 3d 1061, 1063, 473 N.E.2d 584 (1985) (Freeman)), but “is available only when the plaintiff has set forth every material fact needed to prove that he has a clear, legal right and is entitled to the performance of the act he seeks to compel.” Baldacchino, 289 Ill. App. 3d at 109, citing Vanko v. Sheahan, 278 Ill. App. 3d 302, 303, 662 *186N.E.2d 512 (1996). A decision to grant or deny mandamus will be reversed on appeal only when it is against the manifest weight of the evidence. Machinis v. Board of Election Commissioners, 164 Ill. App. 3d 763, 768, 518 N.E.2d 270 (1987); Báldacchino, 289 Ill. App. 3d at 109.
Washington argues that because the Director exercises discretion to determine which inmates are entitled to meritorious good-time awards and the amount of meritorious good time, if any, to award an inmate, the Director’s decision is based on consideration of various factors and is not subject to mandamus. By granting Braver’s petition and ordering him released from IDOC’s custody, the circuit court usurped the Director’s authority, impermissibly exercising the discretion that the legislature gave solely to the Director. He asserts that the Unified Code of Corrections’ language makes clear that there is no entitlement to the type of good-conduct credit involved in this case, namely, meritorious good-time credit. We agree.
II
In the present case, the Director established the discretionary nature of the award, where witnesses McHugh and Schellinger testified that the Director uses his discretion to determine whether to award meritorious good time based on various factors. Affidavits submitted by O’Leary, Boots and Jockisch also established that the Director is not compelled to award meritorious good-time credit to any particular inmate. The evidence submitted by the IDOC officials should not have been ignored; it clearly demonstrated that Braver’s assertion had no basis in fact. Brooks stated that of the 21,611 inmates released from the Department prisons in fiscal year 1997, 4,106 of the inmates received less than 90 days of meritorious good time and 2,194 received no award at all.
Based on the plain language of section 3 — 6—3 of the Unified Code of Corrections, the legislature intended the decision to award meritorious good-time credit to rest within the discretion of the IDOC Director. 730 ILCS 5/3 — 6—3 (West 1996). The circuit court’s decision to grant Braver’s action for mandamus was against the manifest weight of the evidence. Braver had no clear right to an award of meritorious good-time credit, let alone a specific number of days on a specific date. The court’s analysis should have ended there. It did not. Braver failed to establish that IDOC treated similarly situated persons in a dissimilar manner. The IDOC policy, of requiring that an inmate be confined for 30 days before being considered for an award and approximately 60 days before credit is awarded, allows IDOC time to assess each inmate, which includes consideration of pre-IDOC behavior or adjustment based on any documentation received. Such a policy *187helps to ensure that public safety and security are not compromised when an inmate is released early. This cause is, therefore, reversed.
Washington next maintains the circuit court erroneously concluded that the Director’s failure to award Braver meritorious good-time credit violated his right to equal protection. Although this matter has been resolved as to Braver, we consider this due process argument by virtue of its potential application in future cases. The circuit court here acknowledged the discretionary nature of the Director’s decision whether to award meritorious good-time credits, yet based its decision on what it termed “fundamental fairness,” apparently agreeing with Braver’s assertion that the IDOC policy of awarding meritorious good-time credit only after an inmate has been in IDOC custody for about 60 days violated his right to equal protection because it was unfair to those inmates spending pretrial time in county jail, as compared to those individuals out on bond.
Braver asserts that due process and equal protection of the law entitled him to meritorious good time for the period he served in the county jail, emphasizing IDOC’s fundamentally unfair policy of treating indigent and nonindigent inmates differently with respect to its behavior evaluation policy. Pointing out that 90% of IDOC’s inmate population receives meritorious good-time credit, and the absence of written criteria on which to award such credit, he urges that the statistics show the de facto existence of IDOC’s policy of automatically granting meritorious good-time credit to all inmates who receive the usual and ordinary day for day meritorious good-time credit. Braver maintains that IDOC’s admittedly serious administration problem regarding evaluation of inmates’ pre-IDOC incarceration behavior is IDOC’s responsibility to solve and the consequences of those problems should not be placed on the indigent prisoner.
Statutory construction requires that the intention of the legislature be ascertained and given effect; in doing so, courts look first to the statute’s terms. Lane v. Sklodowski, 97 Ill. 2d 311, 316, 454 N.E.2d 322 (1983).2
The award of good-conduct time and the decision to consider such *188an award are discretionary by statute; the Director of IDOC is not required to grant the time or even consider it, absent a clear duty to *189act, which is not present here. Brewer v. Peters, 262 Ill. App. 3d 610, 613, 633 N.E.2d 17 (1994).
The equal protection guarantees of the United States and Illinois Constitutions mandate that state regulations and legislation accord similar treatment to similarly situated persons. U.S. Const., amend. XIV; Ill. Const. 1970, art. I, § 2; Hampton v. Rowe, 88 Ill. App. 3d 352, 354, 410 N.E.2d 511 (1980) (Hampton). In the absence of “the existence of a classification which is inherently suspect or the infringement of a fundamental right, distinctions drawn by a State governmental unit in determining the application of a particular policy must be rationally related to the furtherance of a legitimate governmental interest to comply with the requirements of equal protection.” Hampton, 88 Ill. App. 3d at 355. The standard of review, therefore, when considering an alleged equal protection violation is the rational basis test. Once a discriminatory classification is shown, under the rational basis test the court first must look to the purposes behind the legislative scheme at issue, and then determine whether the classification bears a rational relationship to a legitimate legislative purpose. Hampton, 88 Ill. App. 3d at 355; People v. Miles, 53 Ill. App. 3d 137, 142, 368 N.E.2d 187 (1977).
At issue in the case at bar is the discretionary credit awarded for meritorious service under subsection 3 of section 3 — 6—3(a), not the good-conduct credit automatically earned by a prisoner pursuant to subsection 2.1. In People v. Coleman, 140 Ill. App. 3d 806, 489 N.E.2d 455 (1986), the court noted that “credit for meritorious service under subsection (3) is neither automatically given by statute nor awarded by the Director.” Coleman, 140 Ill. App. 3d at 813. Here, the record demonstrates that Braver’s assumption that all inmates are awarded 90 days of meritorious good-time credit as soon as they have been in custody for about 60 days is unsupportable. The statistics *190show instead that not all inmates receive an award of meritorious good-time credit and those that do do not necessarily receive the full amount allowed pursuant to section 3 — 6—3(a)(3). Nor do they necessarily receive such an award on their sixty-first day of incarceration.
Braver’s reliance on Hampton also is misplaced. There, the circuit court denied the prisoner’s action for mandamus, seeking to compel the Director of IDOC to credit him with compensatory good time for his preconviction confinement in county jail. The circuit court’s decision, finding IDOC’s regulation of giving compensatory credit only to those inmates in IDOC custody, violated Hampton’s right to equal protection because it was not rationally related to a legitimate government purpose, creating a discriminatory classification in that inmates such as Hampton were treated differently because of their pretrial confinement.
Unlike the compensatory good time at issue in Hampton, meritorious good time, as previously stated, is not automatic but is given to all eligible inmates, based upon the Director’s discretion after considering numerous factors. Such an award varies in amount depending on the assessment, with a maximum award being set by section 3 — 6—3.
Further, Freeman, another case upon which Braver relies, is proeedurally distinguishable. In Freeman, this court reversed the dismissal of the petition for writ of mandamus, finding that the prisoner had alleged sufficient facts to state a claim for relief where he alleged that IDOC had an established policy of crediting inmates with meritorious good time on a regular basis. The Director filed a motion to dismiss wherein he addressed only the legal sufficiency of the petition. The court remanded the matter for a hearing on the petition to determine whether IDOC had an established and regular policy of awarding meritorious good time to a certain class of inmates, stating that the petition would be denied if the Director established the discretionary nature of his decision to award meritorious good-time credit.
Therefore, even under an equal protection analysis, requiring an inmate to spend at least 60 days in IDOC custody is rationally related to legitimate government interests. Holding such a procedure, under the foregoing circumstances, as violative of Braver’s due process rights was error, and the circuit court’s decision on this ground is also reversed.
*191For the reasons set forth above, the judgment awarding Braver’s mandamus action must be reversed.
Reversed.
THEIS, EJ., concurs.
