Change in bias in self-reported body mass index in Australia between 1995 and 2008 and the evaluation of correction equations

Using data from large, nationally-representative population health surveys, we examined change in bias in height and weight reporting among Australian adults between 1995 and 2008. Our study dataset included 9,635 men and women in 1995 and 9,141 in 2007-2008. We investigated the determinants of the bias and derived correction equations using 2007-2008 data, which can be applied when only self-reported anthropometric data are available.In 1995, self-reported BMI (derived from height and weight) was 1.2 units (men) and 1.4 units (women) lower than measured BMI. In 2007-2008, there was still underreporting, but the amount had declined to 0.6 units (men) and 0.7 units (women) below measured BMI. The major determinants of reporting error in 2007-2008 were age, sex, measured BMI, and education of the respondent. Correction equations for height and weight derived from 2007-2008 data and applied to self-reported data were able to adjust for the bias and were accurate across all age and sex strata.The diminishing reporting bias in BMI in Australia means that correction equations derived from 2007-2008 data may not be transferable to earlier self-reported data. Second, predictions of future overweight and obesity in Australia based on trends in self-reported information are likely to be inaccurate, as the change in reporting bias will affect the apparent increase in self-reported obesity prevalence.The increasing prevalence of obesity is a major public health concern in most developed countries throughout the world. The most common means of determining obesity in population studies is through the use of body mass index (BMI) determined from weight in kilograms divided by the square of height in meters [1]. Frequently, this is based on self-reported height and weight data, which are necessary in postal or telephone surveys, or because it is impractical or too costly to take actual measurements. However, numerous studies have found that self-reported data tend to overestimate h