Fasting blood sugar was measured in 25 obese adults before and after a 12-week supervised exercise programme. The investigator wants to know whether the mean change within individuals is statistically significant. The differences are approximately normally distributed. Which is the most appropriate test?

• A Independent samples t-test
• B One-way ANOVA
• C Chi-square test
• D Paired t-test ✓

Explanation

The same subjects are measured twice under two conditions, so the observations are paired, not independent. The paired t-test analyses the mean of the within-person differences against zero, which removes between-subject variability and gives greater statistical power than an unpaired comparison on the same data. An independent t-test would wrongly treat the two sets of measurements as coming from separate groups and would violate the assumption of independence.

Reference: Mahajan's Methods in Biostatistics for Medical Students and Research Workers, 9th ed.

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