incorporated into § 216(b) the requirements of current Federal Rule of Civil Procedure 23. See Bayles, 950 F.Supp. at 1060-61 (discussing cases adopting this approach). For example, in Shushan v. University of Colo., 132 F.R.D. 263 (D.Colo.1990), the district court eon- eluded “that Rule 23(a)’s four prerequisites [numerosity, commonality, typicality, and adequacy of representation] and 23(b)(3)’s requirement that common questions of fact predominate should be used to determine whether plaintiffs are similarly situated.” Bayles, 950 F.Supp. at 1061 (describing Shushan holding). In a third approach, district courts have suggested incorporating into § 216(b) the requirements of the pre-1966 version of Rule 23, which allowed for “spurious” class actions. See Bayles, 950 F.Supp. at 1064 (<HOLDING>). Under the pre-1966 version of Rule 23, the
holding that because advisory committee notes to the 1966 amendments make clear that the amendments were not intended to affect  216b actions if rule 23s standards apply  at all it must be through rule 23 as it existed prior to 1966 holding that amendments to procedure apply to both pending and future matters holding that adea class actions are optin actions under  216b not optout actions subject to rule 23 holding that the protect act amendments to the standard of review apply retroactively holding that the 1991 mixedmotive amendments do not apply to  1981 based on an independent analysis of the amendments and  1981