(concurring, with whom Greaney, J., joins). I agree that DuPont’s claims are properly dismissed, but for reasons that differ from those of the court. Strict scrutiny applies to DuPont’s gender-based equal protection claim under the Massachusetts Constitution.1 See art. 1 of the Massachusetts Declaration of Rights, as amended by art. 106 of the Amendments; Commonwealth v. King, 375 Mass. 5, 21 (1977). I write separately because, contrary to the court’s conclusion, ante at 399-403, in my judgment the Department of Correction (department) has failed to establish that for purposes of serious disciplinary sanctions (the critical focus here), male and female prisoners found to have committed “major” incidents are not “similarly situated.” See Barrington Cove Ltd. Partnership v. *404Rhode Island Hous. & Mtge. Fin. Corp., 246 F.3d 1, 8 (1st Cir. 2001) (test is “whether a prudent person, looking objectively at the incidents, would think them roughly equivalent and the protagonists similarly situated”).
A prisoner who is found by a hearing officer to have incited a riot, killed another prisoner, tampered with prison locks, possessed a gun, or taken hostages has committed a “major” disciplinary infraction. See 103 Code Mass. Regs. §§ 430.09, 430.24(7), (14), (15), (16) (1995). Neither the number of other prisoners residing in the disciplinary offender’s institution at the time of the incident nor the underlying crime that caused the offender’s (or other prisoner’s) incarceration are relevant to whether discipline is warranted; the inmate’s actions pose dangers of such gravity that the Commissioner of Correction (commissioner) has identified them as meriting “[m]ajor sanctions.” See 103 Code Mass. Regs. § 430.25(3) (1995).2 “Major” disciplinary offenses always involve a threat to the well-being of others and a threat to the security of the prison in which the person is incarcerated.3 The question here is not whether prison security is jeopardized by such offenses but whether the admittedly starkly different discipline of individual male and female prisoners who commit such “major” disciplinary offenses is permissible.4 Cf. Pitts v. Thornburgh, 866 F.2d 1450 (D.C Cir. 1989) (male and female prisoners “similarly situated” for purposes of determining whether the locations of *405their respective prisons violated equal protection); Glover v. Johnson, 478 F. Supp. 1075, 1077-1078 (E.D. Mich. 1979) (male and female prisoners “similarly situated” for purposes of educational programs).
It is instructive that none of the cases relied on by the court to reach the conclusion that for purposes of discipline male and female prisoners are not similarly situated, see ante at 401-402, deals with the type of disciplinary sanctions at the root of DuPont’s equal protection claim.5 In addition, in every case relied on by the court — all (but one) Federal cases applying Federal law — the courts were not required to subject the gender-based claims to strict scrutiny, as we are required to do under Massachusetts law. See Commonwealth v. King, supra. Moreover, the cases cited by the court rely principally on the highly deferential, rational basis rationale of Turner v. Safley, 482 U.S. 78 (1987), which was explicitly rejected by the Court in Johnson *406v. California, 543 U.S. 499, 509-511 (2005), as inapplicable to equal protection challenges to prison regulations that require heightened scrutiny. See note 6, infra. Because in Massachusetts sex-based classification is, like race-based classification under Federal law, subject to strict scrutiny, it is “immediately suspect,” id. at 509, and because the regulation at issue is a particularly harsh deprivation of liberty, see O’Malley v. Sheriff of Worcester County, 415 Mass. 132, 139 (1993), the high deference to prison officials and reliance on generalized demographic data that may be appropriate for rational basis review is inappropriate here. See Johnson v. California, supra at 512.
Applying the strict scmtiny standard, as we must, I conclude that male and female prisoners are similarly situated for purposes of “major” disciplinary sanctions, and the department must therefore establish that its policy of enforcing its gender-neutral code of prison discipline in a sex-specific manner serves “a compelling interest” and “is limited as narrowly as possible consistent with its proper purpose.” Commonwealth v. Chou, 433 Mass. 229, 237 n.6 (2001), quoting Lowell v. Kowlaski, 380 Mass. 663, 666 (1980). See Attorney Gen. v. Massachusetts Interscholastic Athletic Ass’n, 378 Mass. 342, 354 (1979), citing Commonwealth v. King, supra at 28 (actions must further demonstrably compelling interest, and means employed must be narrowly tailored, consistent with legitimate purpose).
In holding that DuPont’s claim cannot survive the threshold “similarly situated” inquiry, the court considers the prison demographic data offered by the commissioner in his second affidavit sufficient to prove that male and female inmates are not “similarly situated.” See ante at 396-397. However, in reviewing equal protection claims through the lens of heightened scrutiny, courts are required to look beyond justifications of disparate government action purportedly based on objective data. Even where, as in the prison context, the defendant officials are given a wide range of discretion, the reviewing court must train a critical eye on attempts to treat groups differently by suspect classifications. See Johnson v. California, supra at 512 (deference shown to expertise of prison officials in matters of prison operations, but Court will apply strict scmtiny to official policies *407based on suspect classifications).6 Government officials may not use a suspect classification as a “proxy” for individual characteristics or behavior. Id. at 511. Courts are required to take a “hard look” at official distinctions among groups based on their supposedly inherent differences. United States v. Virginia, 518 U.S. 515, 541 (1996) (applying intermediate scrutiny to Federal equal protection claims of females excluded from all-male Virginia Military Institute). Overly broad generalizations about “the way women are,” id. at 550, or “the way men are,” or based on the number of men housed together who may have committed violent crimes, may not serve as the basis to impose special burdens or award special benefits to individual men and women whose actions fall outside the presumed, sex-typed norm.7 Id. The question is not whether DuPont is a bad actor in a bad environment, and “female prisoners” as a group are better people in a better environment, see ante at 398, but whether DuPont and any female prisoner who committed the same major offense as he *408did, thereby threatening public safety and prison security, are similarly situated for purposes of these severe disciplinary sanctions.
As noted earlier, the different treatment of male and female prisoners who commit major disciplinary offenses is stark. The male offender who, for example, stabs another inmate, faces the possibility of up to ten years in the department disciplinary unit (DDU), an especially harsh form of incarceration.8 The female prisoner who stabs a fellow inmate, on the other hand, in all likelihood will serve a maximum of thirty days in solitary confinement. The reason for the vast disparity in punishments for the same obviously brutal and disruptive behavior is not apparent, if gender is not the major or determining criterion for the differing sanctions. Either the stabbing of a fellow inmate is a “major” disciplinary offense or it is not. If it is a major disciplinary offense, the security of the prison is at risk, see notes 2 and 3, supra, and sanctions should be levied on both women and men with something approaching far greater uniformity, as the gender-neutral written disciplinary regulations require. See 103 Code Mass. Regs. § 430.25(3). Generalizations about women’s less aggressive nature,9 comparative data about types of convictions for which men and women are *409imprisoned, the length of their respective sentences, the number of major disciplinary infractions per penal institution, or even prison gang violence do not speak to the reality that individual female and male prisoners may and do act in similarly violent and dangerous ways. Faced with a constitutional challenge to the marked disparity of sanctions between genders, the sex-specific general data submitted by the commissioner are “immediately suspect,” Johnson v. California, supra at 509, raising many more relevant questions than they settle. Rooting out improper motives in the sex-based classification of prisoners “bolsters the legitimacy of the entire criminal justice system.” Id. at 511. It is a goal wholly compatible with the orderly, effective administration of prisons. Id. at 510.
The Legislature could not enact a law providing enhanced penalties for male but not female serial killers on the grounds that women are as a rule less violent than men and commit fewer serial murders, and thus the groups are not substantially similar. Cf. Commonwealth v. King, 374 Mass. 5, 19-22 (1977) (law criminalizing female but not male prostitution offends equal protection guarantees of the Massachusetts Constitution). The same strict scrutiny rationale forbids the department from imposing a far greater punishment on a male inmate than would be incurred by a female inmate who commits the same offense. The department should not have been awarded summary judgment predicated on a lack of substantial similarity between the classifications challenged.
A conclusion that strict scrutiny applies to DuPont’s equal protection claim would not of itself be dispositive; ordinarily it would require remand to the trial court on the merits unless the summary judgment record established beyond dispute that both prongs of the analysis required in strict scrutiny cases, see Commonwealth v. Chou, 423 Mass. 229, 238 (2001), is without factual dispute. The first prong of the strict scrutiny test, that the department demonstrate a compelling interest, is not difficult for the department to surmount: the “compelling” nature of the need of prison officials and the public for orderly and secure prison administration is obvious. See, e.g., Rasheed v. Commissioner of Correction, 446 Mass. 463, 473-474 (2006), citing Cutter v. Wilkinson, 544 U.S. 709, 722-723 (2005) (“It cannot be doubted that the department has a compelling interest *410in ensuring the safety of its staff and its inmates and the integrity of its institutions”). In my judgment, the department has met that burden here. I do not believe, however, that on the record submitted in support of summary judgment, the department has met its burden on the second prong: establishing beyond factual dispute that the challenged policy is “narrowly tailored” to its purpose. In different circumstances than pertain here (DuPont has been released), that question would be resolved at trial.
It is possible that at a trial, the department could prove that it has met the narrow tailoring required of strict scrutiny. It is, for example, within the authority of the commissioner to isolate inmates who, even after being assigned to a maximum security facility, continue to engage in violent or recalcitrant behavior toward either staff or fellow inmates. The commissioner may be able to prove that the operation of the DDU at Massachusetts Correctional Institution at Cedar Junction is not only “consistent with correctional institution management of a maximum security prison,” as he states in his second affidavit, but that lengthy terms of severe isolation for those who commit “major” disciplinary offenses are the only effective way (i.e., the most “narrowly tailored” way) to provide a safe and secure correctional environment for other inmates, correctional staff, and the public in a maximum security prison. The high concentration of particularly dangerous prisoners in a single location may require the commissioner to implement such security measures concomitant with controlling such an environment. But such claims must be subjected to greater scrutiny than a grant of summary judgment on the basis of the commissioner’s conclusory affidavits permits. I am not convinced on the record before us that the commissioner is unable to avail himself of more limited means to ensure prison safety than by disciphning male prisoners with disciplinary problems and female prisoners who commit the same type and number of disciplinary offenses in such grossly different ways.
In this case, DuPont has been released from incarceration. Any inquiries into the merits, including those pertaining to the narrowly tailored prong of the strict scrutiny test, are therefore *411moot.10 The department is entitled for that reason alone to summary judgment as a matter of law. See Acting Supt. of Bournewood Hosp. v. Baker, 431 Mass. 101, 103 (2000), quoting Attorney Gen. v. Commissioner of Ins., 403 Mass. 370, 380 (1988). (“Litigation ordinarily is considered moot when the party claiming to be aggrieved ceases to have a personal stake in its outcome”).
The court notes that strict scrutiny “would likely be the proper standard to apply to gender-based classifications in the prison context.” Ante at 391.
See also 103 Code Mass. Regs. § 430.09(4) (1995) (“In designating the offense as a minor or major matter, the disciplinary officer may consider the following factors: (a) Threat to institutional security; (b) Repetitiveness; (c) Extent of harm done; and (d) Mitigating circumstances”).
See 103 Code Mass. Regs. § 430.09(5) (1995) (“Cases involving little or no threat to the well being of others, to property, or to the security of the institution shall ordinarily but not necessarily be designated as minor matters”).
In his forty-six page handwritten complaint, which was not included in the record on appeal, DuPont alleges, among other things, that he was consigned to the department disciplinary unit (DDU) on charges of having violated an unwritten prison policy limiting haircuts to fifteen minutes, a “minor” incident in any case. He also alleges that assignment to the DDU was in retaliation for prior litigation he had filed against the department. DuPont also asserts that, while confined in the DDU, he was in “[ijsolation for over 2½ years with no personal property, no tv, no radio, no incoming mail stamps, no personal visits, no telephone calls, no canteen, no programs . . . .”
See Oliver v. Scott, 276 F.3d 736, 743-746 (5th Cir. 2002) (policy of permitting female guards to strip search male inmates and monitor them in showers; lack of partitions in male but not female prison bathrooms); Keevan v. Smith, 100 F.3d 644, 647-651 (8th Cir. 1996) (prison demographics justify offering fewer educational and job-training programs for female prisoners than male prisoners); Women Prisoners of D.C. Dep’t of Corrections v. District of Columbia, 93 F.3d 910, 923-927 (D.C. Cir. 1996), cert. denied, 520 U.S. 1196 (1997) (rejecting program-by-program comparisons of vocational and other programs in male-only and female-only prisons because, inter alla, women’s prisons were smaller and contained programs not available in men’s prisons, and inmates have no constitutional rights to work and educational opportunities); Klinger v. Department of Corrections, 31 F.3d 727, 731-734 (8th Cir. 1994), cert. denied, 513 U.S. 1185 (1995) (differences in prison programs and services between men’s and women’s prisons permitted in light of different attributes of respective prisons and broad discretion permitted prison officials); Timm v. Gunter, 917 F.2d 1093, 1098-1099 (8th Cir. 1990), cert. denied, 501 U.S. 1209 (1991) (opposite-sex surveillance and pat searches of male inmates justified, in part, by need for optimum uses of security resources and the superior rights of female prison guards to equal employment opportunity); Pargo v. Elliott, 894 F. Supp. 1243, 1263 (S.D. Iowa), affd, 69 F.3d 280 (8th Cir. 1995), cert. denied, 519 U.S. 831 (1996) (finding, inter alla, heightened analysis inapplicable to claims of disparities in programs and services between men’s and women’s prisons).
The only case that bears any factual similarity to this case is State v. Emery, 357 A.2d 878 (Me. 1976). There, the Supreme Judicial Court of Maine determined that, for purposes of punishing prison escape attempts, male and female inmates were not similarly situated. However, the opinion turned on legislative distinctions between “inmates” and “prisoners” and between State prisons and the women’s correctional center. See id. at 880.
The defendants’ brief makes no mention of Johnson v. California, 543 U.S. 499 (2005), which held that an unwritten prison policy of separating new and transferring prisoners by race violated the equal protection guarantees of the Fourteenth Amendment to the United States Constitution. Perhaps this is because in that case all of the male inmates were held in the same maximum security prison, and were separated from one another under a nonfacially neutral regulation solely on the basis of their race. Id. at 502-503. Here, the regulation is facially neutral, and there is no challenge from DuPont that the separation of men and women into different prisons is impermissible even under a strict scrutiny standard. See G. L. c. 127, § 20. However, the defendants’ reliance on Turner v. Safley, 482 U.S. 78 (1987), and their argument that rational-basis scrutiny, with its highly deferential standard of review, should apply to DuPont’s claims is misplaced. In Johnson v. California, supra, the Supreme Court explicitly rejected the premise that the Turner case was applicable to cases involving suspect classifications. (“Turner is too lenient a standard to ferret out invidious uses of race”). At least in this Commonwealth, where gender classifications (like race classifications in the Federal system) are subject to strict scrutiny, prison cases involving gender classifications should be viewed under the standard of Johnson v. California, supra at 513, and not under the standard of Turner v. Safley, supra. See Commonwealth v. King, 374 Mass. 5, 21 (1977).
I recognize that, for purposes of equal protection analysis, courts must distinguish between government action that burdens an already disfavored class and government action intended “to hasten the day when entrenched discrimination and its aftereffects have been extirpated.” Gratz. v. Bollinger, 539 U.S. 244, 301 (2003) (Ginsburg, J., dissenting). See Brackett v. Civil Serv. Comm’n, 447 Mass. 233, 251-252 (2006). The point requires no further development here, where DuPont’s equal protection claim is moot. See infra.
In earlier litigation we observed that inmates in the DDU are permitted only three showers weekly and five hours of outdoor exercise weekly, weather permitting. For the remainder of the week, they are confined to a seven by twelve foot, minimally furnished cell, and their contact with the outside world may be severely limited. See Torres v. Commissioner of Correction, 427 Mass. 611, 613, cert denied., 525 U.S. 1017 (1998). See also note 4, supra, describing DuPont’s severe conditions of confinement in the DDU, which are not challenged by the department.
Although the commissioner points to women’s supposedly less aggressive nature to justify his differential enforcement of gender-neutral disciplinary sanctions, he has also conceded that at least some women have committed disciplinary infractions serious enough to warrant their transfer to maximum security facilities out of State. See ante at note 22. The commissioner does not disclose for how long or under what conditions such female prisoners are confined. To the extent that the female prisoners are transferred for purposes of administrative convenience rather than placed in a DDU for women, administrative convenience without more is not a proper ground to justify gender-based differential treatment. Cf. Stanley v. Illinois, 405 U.S. 645, 656 (1972) (applying intermediate scrutiny to gender-based equal protection claim). It is also clear from the commissioner’s affidavit that not all DDUs need necessarily be housed in maximum security facilities.
DuPont’s complaint requested, among other things, declaratory and injunctive relief, as well as damages under G. L. c. 93, § 102, on his equal protection claims. On appeal, he does not press the statutory claim.