ABSTRACT
Educational researchers may be less familiar with nonparametric methods and in particular rank test procedures than with parametric methods. Use of nonparametric rank procedures is more common among research psychologists. In this chapter, six nonparametric or distribution free statistics that make use of rank scores are introduced: Spearman’s correlation, Run’s test, Wilcoxon M-W test, Signed ranks test, Kruskal Wallis ANOVA and Friedman’s ANOVA. The term distribution free is strictly not accurate. Whereas parametric statistical procedures are dependent upon distributional theory, they make certain specific assumptions about patterns of variability in the population (referred to as statistical test assumptions). Nonparametric tests do not rely on population distributional assumptions. Nonparametric procedures are not entirely distributional free. Whilst not making use of distribution theory in the same way that parametric procedures do, (mathematical descriptions of patterns of variation are used to make inferences about population parameters or constants based on sample data) they nevertheless definitely do make use of the distribution of sample observations. In this sense they are not distribution free.
