stevenson-methodologicalproblem-2011.pdf (340.01 kB)
Methodological problem with comparing increases in different measures of body weight
journal contribution
posted on 2011-05-23, 00:00 authored by H Walls, Anna PeetersAnna Peeters, H Mannan, Christopher StevensonChristopher StevensonBackground: A 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.
Findings: The 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.
Conclusion: Differences 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.
Findings: The 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.
Conclusion: Differences 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.
History
Journal
BMC research notesVolume
4Issue
145Pagination
1 - 3Publisher
BioMed CentralLocation
London, Eng.Publisher DOI
ISSN
1756-0500Language
engPublication classification
C1.1 Refereed article in a scholarly journal; C Journal articleCopyright notice
2011, Walls et al.Usage metrics
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