Some recurrent problems in interpreting statistical evidence in equal employment cases

Although the U.S. Supreme Court accepted statistical evidence in cases concerning discrimination against minorities in jury pools and equal employment in 1977, several misinterpretations of the results of statistical analyses still occur in legal decisions. Several of these problems will be described and statistical approaches that are more reliable are presented. For example, a number of opinions give an erroneous description of the p-value of a statistical test or fail to consider the power of the test. Others do not distinguish between an analysis of a simple aggregation of data stratified into homogeneous subgroups, and one that controls for subgroup membership. Courts have used measures of 'practical significance' that lack a sound statistical foundation. This has led to a split in the Circuits concerning the appropriateness of 'practical' versus 'statistical' significance for the evaluation of statistical evidence.