Statistical Proof and Theories of Discrimination

Barbara Norris's article explains the relationship among disparate treatment theory, disparate impact theory, and multiple regression.' It is a powerful combination. It is altogether too powerful; it proves far too much. The basic crunch on employers comes from the combination of the disparate treatment and disparate impact theories. Disparate treatment theory requires employers to hire randomly or on some measure of merit. Most choose merit, at least in part. But disparate impact theory is suspicious of all measures of merit; employers must justify each measure used with prohibitively expensive validation studies. The combination is a great onetwo punch for plaintiffs: charge the employer with disparate treatment, and when he explains the rejection of women or minorities with measures of merit, charge him with disparate impact on the basis of each and every defense. This strategy has been available since Griggs v. Duke Power Co.2 I have been telling my students about this for years, and Sullivan, Zimmer, and Richards put it in their treatise.3 Lots of plaintiffs' lawyers also must have thought of it. Barbara Norris suggests that Segar v. Smith4 is the first opinion to set out the whole scheme. That is surprising, if true. Statistical evidence greatly increases the power of this analytic scheme. With statistics, a plaintiff can raise a strong presumption of disparate treatment without examining the qualifications of a single employee or applicant. But there are unexamined assumptions in this approach. All statistical techniques depend on technical assumptions that are rarely met in the real world. Indeed, a good technique for defense lawyers is to hire mathematical statisticians, generally found in university departments of statistics or mathematics, who will often testify that none of the assumptions are met and plaintiff's statistics prove nothing. Some of these experts seem to think the assumptions are never met and statistics are entirely useless for any purpose; such views are apparently a source of prestige among