A researcher ranks 50 medical students by their class attendance and separately by their internal assessment scores, then wants to measure the association between the two sets of ranks. The relationship appears consistently monotonic but not linear. Which correlation measure is most appropriate?

• A Pearson correlation coefficient
• B Regression coefficient
• C Coefficient of determination
• D Spearman rank correlation coefficient ✓

Explanation

Spearman's rank correlation works directly on ranked data, makes no assumption of linearity or normality, and detects any consistent monotonic relationship. Pearson's product moment correlation assumes both variables are measured on an interval scale and quantifies specifically linear association, so it is unsuited to ordinal rank data with a non-linear trend, which is the key distractor here.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

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