Haemoglobin values have a mean of 12 g/dL with SD 1.2 g/dL, while serum creatinine values in the same cohort have a mean of 1 mg/dL with SD 0.25 mg/dL. To decide which variable shows greater relative variability, the statistic to compare is:

• A Range
• B Standard error of mean
• C Interquartile range
• D Coefficient of variation ✓

Explanation

Absolute measures like SD cannot be compared across variables with different units or widely different means. The coefficient of variation expresses SD as a percentage of the mean, giving 10% for haemoglobin and 25% for creatinine, so creatinine is relatively more variable despite its tiny SD. Standard error describes precision of the mean estimate, while range and interquartile range remain unit-bound absolute measures unsuited to cross-variable comparison.

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

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