Using relative distributions to investigate the body mass index in England and Canada.

In this paper we use relative distributions to examine changes in the distribution of the body mass index (BMI) in England and Canada during the period 1994/5-2000/1. The use of relative distributions allows us to describe changes in the whole distribution of the BMI in a non-parametric fashion. While statistics analogous to the Gini index can be constructed based on the relative distribution, important characteristics of changes in the distribution of the BMI such as changes in the proportions overweight and obese are more naturally handled using measures of relative polarization. Our results show that while BMI has increased in both countries, BMI in England has increased at a much faster rate than in Canada. Both groups show polarization over time towards both tails of the weight distribution, with the English polarizing towards the upper tail at a faster rate than Canadians. Copyright (c) 2007 John Wiley & Sons, Ltd.