A researcher compares the variability of haemoglobin levels (mean 12 g/dL, SD 1.2 g/dL) with that of systolic blood pressure (mean 120 mmHg, SD 12 mmHg). Which statistic allows a valid direct comparison of relative variability between these two variables?

• A Standard error of the mean
• B Range
• C Variance
• D Coefficient of variation ✓

Explanation

The coefficient of variation, calculated as (SD divided by mean) multiplied by 100, expresses variability in percentage terms and is unit free. It is the correct tool when comparing dispersion across variables measured in different units or with very different means. Both datasets here have a CV of 10%, so their relative variability is identical, a fact the raw SDs cannot reveal because the units differ.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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