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Research by Maynooth University Economist Professor Donal O'Neill is featured in a recent Irish Times article exploring the difficulties associated with measuring obesity. The Irish Times article titled "Are Irish Rugby Players Too Fat?" discusses problems associated with Body Mass Index, the traditional way of measuring obesity.
The article features research by Professor O'Neill titled "Measuring obesity in the absence of a gold standard" published Economics and Human Biology and available here.
Professor O'Neill's research uses latent class statistical analysis to characterise three measures of obesity in terms of error rates. Utilising data on a nationally representative survey of 33,994 U.S. citizens the research demonstrates that while Body Mass Index (BMI) and Bioelectrical Impedance Analysis (BIA) misclassify large numbers of individuals, this is not the case when Waist Circumference (WC) is used.
This research methodology has been used elsewhere in biostatistics, for example when comparing alternative skin tests for the presence of tuberculosis, comparing diagnosis of myocardial infarction, and evaluating diagnostic tests of autism. However, this is the first application of this approach to measuring obesity.
Starting from the hypothesis that there is no strong basis for choosing any single measure of obesity as a gold standard, the study looks at how competing measures give conflicting results in the same patients and examines the patterns of responses across the entire sample to estimate the underlying error rates of each test. In particular, the estimated error rates are chosen so that the predicted patterns from the underlying model are consistent with the patterns observed in practice. The statistical analysis provides estimated error rates of 3% for Waist Circumference compared to error rates as high as 45% – 50% with BMI and BIA.
The findings have important policy implications, both in terms of how we measure the growth in obesity over time and also in terms of how we evaluate racial gaps in obesity. Since our analysis suggests that measures based on waist circumference accurately reflect the true prevalence of obesity and since waist circumference measures of obesity have grown in excess of what would be predicted given the growth in body mass index it is quite possible that we are underestimating the extent to which obesity has grown over time.
The fact that the Maynooth University study identifies Waist Circumference as an effective measure of obesity has important implications for the understanding of the growth in obesity over the last 20 years. Waist Circumference values through the years have increased beyond those expected from BMI increases and since Professor O'Neill's analysis suggests that the true prevalence rate is reflected in Waist Circumference measures of fatness, this would suggest that the growth in obesity and associated costs may in fact be even more serious than that documented by rising BMI.