ertification stage, Comcast, 133 S. Ct. at 1433, as "reliance on unverifiable evidence is hardly better than relying on bare allegations," Unger v. Amedisys, Inc., 401 F.3d 316, 324 (5th Cir. 2005) . District courts must probe the validity of statistical evidence, as "any method of measurement" would ot