Statistical Advisor, How To Compare Several Variables or Repeated Measures

Nonparametric Distributions

Nonparametric Distributions describes two so-called nonparametric tests for comparing variables. Compared to parametric tests (t-test, ANOVA), nonparametric tests are based on less restrictive assumptions about the nature and distribution of the variables in the comparisons. For example, there are several tests for variables containing only rank order information. Such data may arise, if one asks respondents in a consumer survey to rank order their preferences for several competing brands of soap.

If your data consist of rank orderings, use the Friedman analysis of variance test. If your data are categorical in nature, for example, contains codes identifying one of two possible choices that each respondent made (repeatedly), use the Cochran Q test.

Graphical Analytic Techniques

Graphical analytic techniques include numerous facilities for producing histograms, line graphs, scatterplots, etc., simultaneously for more than one variable. These graphs offer a wide variety of methods to visualize differences between variables.