Stratification and the Adjusted Chi-Square Statistic: Application to Analysis of Employment Discrimination Data

SYNOPTIC ABSTRACT

In this paper we describe and illustrate the concept of “stratification of data” to enhance inferential validity when evaluating rates in employment discrimination lawsuits. Stratification is a means of avoiding confounding effects when classes of employees are distributed differently with respect to variables that correlate with the main variable of interest (e.g., promotions). The summary chi-square statistic developed by Mantel and Haenszel may be helpful when data are stratified, but a threshold consideration of second-order interactions is required. Two alternatives to chi-square are considered, Fisher's exact test and Wilcoxon's signed-rank test. The problem of choosing the appropriate significance level is also considered, with a recommendation. Data from actual lawsuits are used in the illustrations.

Key Words and Phrases:

• stratification
• chi-square
• higher-order interactions
• Fisher's exact test
• signed-rank test
• confounding variables
• employment discrimination litigation
• contingency table analysis