Wal-Mart Stores, Inc. v. Dukes, U.S. 131 S.Ct. 2541 (2011) involved "one of the most expansive class actions ever," with a plaintiffs' class of 1.5 million current and former employees of the store who alleged that "the discretion exercised by their local supervisors over pay and promotion" discriminated against women. (Wal-Mart, supra, 131 S.Ct. at p. 2547.) The plaintiffs' theory was that a discriminatory corporate culture infected the discretionary decision-making of thousands of Wal-Mart managers leading to pay and promotion decisions disproportionately favoring male employees. (Id. at p. 2548.) As evidence there were questions of law and fact common to the plaintiffs' class, the plaintiffs offered (insofar as relevant here) (1) statistical evidence about pay and promotion disparities between male and female employees, and (2) anecdotal reports of discrimination from about 120 female employees. (Id. at p. 2549.) The court evaluated this evidence and found it insufficient under the following standard: certification of the case as a class action required " 'significant proof' " that Wal-Mart operated under a general policy of discrimination. (Id. at p. 2553.) The statistical evidence consisted of a regression analysis conducted at the named plaintiffs' behest, using regional and national data, comparing the number of women promoted into management positions with the percentage of women in the available pool. (Wal-Mart, supra, 131 S.Ct. at p. 2555.) The study found significant disparities that could only be explained by gender discrimination, according to the study's authors. (Ibid.) The court found this evidence about disparities at the regional and national level did not establish the existence of disparities at individual stores or raise any inference of a companywide policy of discrimination implemented by discretionary decisions made at the store level. (Ibid.) Because the Wal-Mart plaintiffs had identified no alleged discriminatory practice other than delegated discretion, the court found merely showing that such discretion produced an overall sex-based disparity was insufficient. (Id. at pp. 2555-2556.) It found the anecdotal evidence even weaker in that regard since the evidence encompassed only a tiny fraction of Wal-Mart's employees and stores, concentrated in a relative handful of states, which failed to demonstrate the company operated under a general policy of discrimination. (Id. at p. 2556.)