Which t-test is used for comparing two related samples, such as pre- and post-test measurements on the same group?

• A. Chi-square test
• B. Pearson correlation
• C. Independent samples t-test
• D. Paired/Dependent samples t-test

Answer: (D)

When you have two related measurements from the same individuals, such as pre- and post-test scores for the same group, you use a paired (dependent) samples t-test. This approach analyzes the differences within each person, so it controls for differences between individuals and focuses on the average change. By calculating the mean difference and the standard deviation of those differences, the test determines whether the average change is significantly different from zero. The main assumptions are that the measurements are on a continuous scale, the two measurements are truly paired for each subject, and the difference scores are approximately normally distributed (with larger samples the test is more forgiving).

Other tests don’t fit this situation: the chi-square test is for categorical data; Pearson correlation measures the strength of association between two continuous variables rather than whether their means differ; the independent samples t-test compares means between two unrelated groups, which isn’t appropriate when the two samples are linked within subjects.