Measurement error and ethnic comparisons of measures of abdominal obesity
Introduction
The rising prevalence of obesity in most nations is causing an increased burden of diabetes, cardiovascular diseases and certain cancers (World Health Organisation, 1998). The measurement of obesity is under review because of increasing evidence that the distribution of body fat and specifically central or abdominal obesity is more important than the degree of excessive weight for a given height, as assessed by the Body Mass Index (BMI). The waist circumference (WC) and its refinement, the waist to hip ratio (WHR), are preferred predictors of the metabolic syndrome (Snijder et al., 2004), type 2 diabetes (Wang et al., 2005) and cardiovascular risk (Megnien et al., 1999, Chen et al., 2007). A very large cross-sectional study of risk factors associated with acute myocardial infarction has confirmed that measures of central obesity and specifically the waist to hip ratio show a much stronger association with coronary heart disease than BMI, increasing the population attributable risk of obesity by more that 3 fold across all ethnic groups (Yusuf et al., 2005). Prospective studies (de Koning et al., 2007, See et al., 2007), including our own (Welborn et al., 2003, Welborn and Dhaliwal, 2007, Dhaliwal and Welborn, 2009), also demonstrate the superiority of WHR and to a lesser extent WC over BMI. The global burden of obesity is considerably underestimated by BMI. But there is a lack of substantive epidemiological data on WC or WHR in ethnic groups, and the technologies are not standardized. Very little has been reported on the precision and reproducibility of the methods used.
This study uses repeated measures of WC and WHR from the Australian Risk Factor Prevalence Study of 1989 to evaluate the precision error of these techniques. The relative utility of WC and WHR will also be assessed in relation with comparisons across ethnic groups and with implications for specific standards in assessing obesity.
Section snippets
Methods
The third Australian Risk Factor Prevalence Study conducted in 1989 by the National Heart Foundation of Australia (Bennett and Magnus, 1994) recruited residents aged 20–69 years who, were registered on the Commonwealth electoral rolls of December 1988 from nine metropolitan cities across Australia: North Sydney, South Sydney, Melbourne, Brisbane, Adelaide, Darwin, Hobart, Perth and Canberra. Subjects were chosen by systematic probability sampling of sex and 5 year age groups. Representative
Measurements
Physical measurements included a single record of height and weight in light summer clothing without shoes. Height was measured to the nearest centimetre and weight to the nearest tenth of a kilogram (1 kg was deducted from actual weight as an allowance for the clothing). The Body Mass Index (BMI) was calculated, being the weight (in kilograms) divided by the height (in metres) squared. Strictly standardized methodologies were followed while measuring waist and hip circumference (Alexander and
Statistical analysis
Measurement error and within subjects % coefficient of variation of the repeated measurements of obesity measures (waist circumference and waist to hip ratio) and blood pressures values were calculated (Bland and Altman, 1986). The measurement error is used to determine the changes that will be considered significant in clinical practice, and is defined by the British Standards Institution as the value below which the absolute difference between two measurements will lie with 95% probability (
Ethical approval
Australian Institute of Health Interim Ethics Committee, following a consultation with the Commonwealth Privacy Commissioner issued the ethics approval for the 1989 survey. The current Ethics Committee of the Australian Institute of Health and Welfare approved the analysis of the survey data.
Results
The baseline characteristics, measures of obesity and country of birth for the 9279 subjects who participated in the 1989 survey are summarized in Table 1. The survey consisted of 4552 males and 4727 females with age range from 20 to 69 years. About 95% of the subjects were born in Australia, United Kingdom and Ireland, Northern Europe, Southern Europe and Asia.
The precision error of waist circumference, hip circumference, waist to hip ratio, systolic and diastolic pressure in both male and
Discussion
This report uses the Australian population data to evaluate the precision error in waist circumference measurements and waist–hip ratio and to compare these measures across various ethnic groups. Our findings confirm waist to hip ratio as a superior measure of central obesity as its measurement error was not associated with the size of the individual as compared to waist circumference. WHR also showed a high degree of precision, similar to that of waist circumference in both males and females.
Conflict of interest statement
The authors have no conflict of interest to declare.
Acknowledgments
The authors are grateful to the National Heart Foundation of Australia for permission to use data from the 1989 Risk Factor Prevalence Survey. We would like to thank Thaila Bejoy for her research and administrative assistance, especially in relation to sourcing the papers and referencing.
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