Chris Elliott makes three errors in the letter about body mass index (BMI) (17 December 2005, p 22).
First, it is indeed counter-intuitive that BMI is a function of the square of height when humans are three-dimensional. However, BMI as a measure of healthy weight-for-height was not based on a model, but on actual mortality data and assessment of which relationship of height and weight was most associated with longevity. While there might be questions about how good that fit actually is, or whether it oversimplifies, it would not be right to discount it altogether simply on the grounds that it doesn't seem to make sense. As John Lee says in his letter in the same issue, "the fact that a mechanism is not obvious at the time can never be used to negate a finding".
Secondly, rowers and coxes are not just scaled versions of each other: a (tall) ...
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