Wal-Mart (D) operates approximately 3,400 stores and employs more than one million people. Local store managers may increase the wages of hourly employees (within limits) with only limited corporate oversight. As for salaried employees, such as store managers and their deputies, higher corporate authorities have discretion to set their pay within pre-established ranges. D permits store managers to apply their own subjective criteria when selecting candidates as 'support managers,' which is the first step on the path to management. Admission to management training requires that a candidate meet certain objective criteria, including an above-average performance rating, at least one year's tenure in the applicant's current position, and a willingness to relocate. Regional and district managers have discretion to use their own judgment when selecting candidates for management training. Dukes (Ps) represent the 1.5 million members of the certified class, who allege that the company discriminated against them on the basis of their sex by denying them equal pay or promotions, in violation of Title VII. Ps claim that their local managers' discretion over pay and promotions is exercised disproportionately in favor of men, leading to an unlawful disparate impact on female employees. Ps claim that the discrimination to which they have been subjected is common to all D's female employees. Ps claim that strong and uniform 'corporate culture' permits bias against women to infect, perhaps subconsciously, the discretionary decisionmaking of each one of D's thousands of managers-thereby making every woman at the company the victim of one common discriminatory practice. Ds moved the District Court to certify the class consisting of '`all women employed at any D domestic retail store at any time since December 26, 1998, who have been or may be subjected to Wal-Mart's challenged pay and management track promotions policies and practices. Ps relied chiefly on three forms of proof: statistical evidence about pay and promotion disparities between men and women at the company, anecdotal reports of discrimination from about 120 of Wal-Mart's female employees, and the testimony of a sociologist, Dr. William Bielby, who conducted a 'social framework analysis' of D's 'culture' and personnel practices, and concluded that the company was 'vulnerable' to gender discrimination. The District Court granted Ps' motion and certified their proposed class. The Court of Appeals affirmed the District Court's certification order. The Supreme Court granted certiorari.