Haemoglobin values in a sample have a mean of 12 g/dL with SD of 1.5 g/dL. Body weights in another sample have a mean of 60 kg with SD of 9 kg. To decide which variable shows greater RELATIVE variability, the appropriate statistic is:

• A Standard deviation
• B Range
• C Variance
• D Coefficient of variation ✓

Explanation

The coefficient of variation equals SD divided by mean, multiplied by 100, giving unit-free relative variability. Here haemoglobin has CV = (1.5/12)x100 = 12.5%, while body weight has CV = (9/60)x100 = 15%, so weight is relatively more variable despite its smaller absolute SD. Raw SD, variance and range carry units, so they cannot fairly compare measurements expressed in different units such as g/dL and kg.

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

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