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BMC Research Notes

, 4:145

First Online: 23 May 2011Received: 23 July 2010Accepted: 23 May 2011DOI: 10.1186-1756-0500-4-145

Cite this article as: Walls, H.L., Peeters, A., Mannan, H. et al. BMC Res Notes 2011 4: 145. doi:10.1186-1756-0500-4-145


BackgroundA number of studies have compared proportional increases over time in waist circumference WC and body mass index BMI. However this method is flawed. Here, we explain why comparisons of WC and BMI must take into account the relationship between them. We used data from two cross-sectional US surveys NHANES 1988-94 and 2005-06, and calculated the percentage change in the average BMI and the average WC between the two surveys, comparing the results with a regression analysis of changes in WC relative to BMI.

FindingsThe crude percentage change in BMI 5.8% was marginally greater than for WC 5.1%. But these percentages cannot be directly compared, as the relationship between the measures is described by a regression equation with an intercept term that does not equal zero. The coefficient of time from the regression equation will determine whether or not WC is on average larger for a given BMI at the second compared with the first time point.

ConclusionDifferences in the percentage change in WC and the percentage change in BMI cannot be usefully directly compared. Comparisons of increases in the two measures must account for the relationship between them as described by the regression equation.

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Autor: Helen L Walls - Anna Peeters - Haider Mannan - Christopher Stevenson


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