APA Dictionary of Psychology

a theoretical probability distribution widely used in the analysis of variance, multiple regression, and other statistical tests of hypotheses about population variances. It is the ratio of the variances of two independent random variables each divided by its degrees of freedom. In an analysis of variance, for example, the F distribution is used to test the hypothesis that the variance between groups is significantly greater than the variance within groups, thus demonstrating evidence of some differences among the means. See F ratio; F test.