Why is the body mass index calculated as mass/height², not as mass/height³?

Burton, R.F. (2007) Why is the body mass index calculated as mass/height², not as mass/height³? Annals of Human Biology, 34(6), pp. 656-663. (doi: 10.1080/03014460701732962) (PMID:18092209)

Abstract

Background: The body mass index or BMI, mass/height2, is used to predict fatness and health. It is an approximation to the Benn index, mass/heightp, where p (typically 1.1–2.5 for adult populations) makes the index uncorrelated with height. Mass/height3 is an index of body build that is independent of scale and statistics. Aim: To explain why p varies and is less than three, show how statistical methods can distort perceptions of mass–height relationships, and clarify the nature of the BMI. Methods: A hypothetical adult population is modelled statistically, with mass being approximately proportional to height3 and with neither variable determining the other. Values of p are calculated both for the model and for real adults. Results: In both cases p increases with the correlation between mass and height. Both p and that correlation are usually lower for women than for men. Conclusions: In adult populations mass must vary more nearly with height3 than with height2, although, for reasons explained, conventional statistical techniques suggest otherwise. Nevertheless the BMI is a valid predictor of fatness from mass and height in adults and is properly divisible into fat mass and fat-free mass indices. The validity of the latter three indices for children is questionable.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Burton, Dr Richard
• Authors: Burton, R.F.
• College/School: College of Medical Veterinary and Life Sciences > School of Life Sciences
• Journal Name: Annals of Human Biology
• Publisher: Taylor & Francis
• ISSN: 0301-4460
• ISSN (Online): 1464-5033