When should a paired samples t-test be used?

• A. When comparing two independent groups.
• B. When samples are more than two groups.
• C. When there are two related observations from the same participants under different conditions.
• D. When comparing two unrelated variables.

Answer: (C)

Paired measurements from the same participants are used when the two observations are related, so the data are dependent. In a paired samples t-test you examine the difference between the two conditions for each person and then test whether the average of those differences is different from zero. This approach leverages the fact that each person serves as their own control, which reduces individual variability and increases the sensitivity to detect a true effect of the condition change. It’s the right choice for two related observations from the same people under different conditions, such as a pre-test and post-test or measurements under two linked states. If the data come from two independent groups, you’d use an independent-samples t-test; for more than two groups, ANOVA; and for assessing the relationship between two variables rather than a mean difference, correlation or regression would be appropriate.