Without evidence of an edict from the company's top brass specifically saying women shouldn't be paid as much or promoted as frequently as their male counterparts, the case will likely rest on statistical proof that women and men are not given the same opportunities at Wal-Mart...Wal-Mart argues that the plaintiffs make compiled "aggregation" errors in their analysis. By combining all of the information on pay in one set of data, the plaintiffs gloss over differences in geography, store size, department and other factors that determine pay.