Analysis of Ordinal Data to Detect Population Differences

The performance of selected parametric and nonparametric tests of location and scale differences are compared on the basis of sampling results from simulated populations of Likert-scale response ordinal data. Additionally, an omnibus test of distributional equality was examined. Type I and Type II error rates for all procedures examined do not indicate any clear-cut superiority for either type of test (parametric vs. nonparametric). Moreover, when sampling from disparate populations, the nonparametric tests of median equality are as sensitive to heterogeneous variances as the parametric test of mean equality.