Number of Samples
Once you have identified the scale of measurement of the dependent variable, you want to determine how many samples or "groups" are in the study design. Designs for which one-sample tests (e.g., Z test; t test; Pearson and Spearman correlations; chi-square goodness-of-fit) are appropriate collect only one set or "sample" of data. There must be at least two sets of scores or two "samples" for any statistic that examines differences between groups (e.g. , t test for dependent means; t test for independent means; one-way ANOVA; Friedman ANOVA; chi-square test of independence) .