Two Measurements, One Question: Which Test Fits Your Data? You measured the same people twice — before and after a training course, at baseline and follow-up, under two conditions — and now you need to know whether the scores really changed. Two tests compete for this job in SPSS: the paired-samples t-test and the Wilcoxon
A p-value tells you whether a difference is statistically significant. It does not tell you whether that difference is big, small, or worth caring about. That is the job of an effect size — and it is the number examiners, reviewers, and journal editors increasingly expect to see next to every p-value in your results
When do you need the chi-square test of independence? You have two categorical variables and one nagging question: are they related? Does beverage preference differ between men and women? Is smoking status associated with education level? Is defect type linked to the factory shift that produced it? Whenever both variables are categories — not numbers,