Group A has haemoglobin values with mean 12 g/dL and SD 1.2 g/dL. Group B has body weights with mean 60 kg and SD 9 kg. To decide which group shows greater relative dispersion, the statistic to compute is:

• A Coefficient of variation in each group ✓
• B Standard error of the mean in each group
• C Range in each group
• D Interquartile range in each group

Explanation

Coefficient of variation is SD expressed as a percentage of the mean, and it is unit free, so it allows comparison of relative variability across variables measured in different units. Here CV is 10 percent for haemoglobin and 15 percent for weight, so weight is relatively more variable. Comparing SDs directly, as a student tempted by option B might, is meaningless when the means and units differ between the two datasets.

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

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