Using effect size measures to reform the determination of adverse impact in equal employment litigation

A critical issue in large-scale employment discrimination litigation is whether the challenged practices have a systematic adverse impact on protected groups of applicants or employees. The methods that are currently used to detect adverse impact are seriously flawed, but these flaws could be addressed by putting more emphasis on commonly used research statistics that measure effect size, such as standardized difference (d) or the percentage of variance (PV) explained. We recommend incorporating these indices as a baseline for detecting the presence of adverse impact, and that when PV or d is small, observed group differences should not be taken as evidence of adverse impact, regardless of the results of significance tests. Such an approach eliminates spurious charges of unfair discrimination, spares employers and the courts from dealing with claims that are frivolous and based on minutia, and helps enforcement agencies to concentrate their efforts on employment practices that are truly discriminatory. More generally, it will improve the use and interpretation of statistical evidence in litigation.