A researcher studying hemoglobin levels in a population with highly skewed distribution including several extreme outliers wants to compare values between two groups. Which measure of central tendency and which non-parametric test are most appropriate, respectively?
- A Mean; Student's t-test
- B Mode; Chi-square test
- C Median; Mann–Whitney U test ✓
- D Median; Paired t-test
Correct answer: C. Median; Mann–Whitney U test
Explanation
In skewed distributions or when outliers are present, the median is the preferred measure of central tendency because it is not influenced by extreme values. The Mann–Whitney U test (Wilcoxon rank-sum test) is the non-parametric equivalent of the independent samples t-test, appropriate when data are not normally distributed. Paired t-test is for matched/before-after data. Chi-square tests categorical data. Mean is distorted by outliers in skewed data.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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