The relationship between observations on two qualitative variables is often referred to as associations between the variables. Observations on two variables obtained from a cohort of subjects are analyzed. Like the evaluation of relationship between observations on two quantitative variables, one variable is designated the outcome, response, or dependent variable, and the other the explanatory, predictor, or independent variable. The cohort of subjects are divided into sub-cohorts by attributes of the explanatory variable. Association between the two variables is assessed by comparing the distributions of the observations on the outcome variable among sub-cohorts of subjects specified by attributes of the explanatory variable.