Overweight and obesity in Australia: an underestimate of the true prevalence?

In reply: Coyne suggests that, based on comparisons within Queensland, the national prevalence of obesity in our article1 is an underestimate. It should be noted that the Australian Diabetes, Obesity and Lifestyle Study (AusDiab) was designed primarily to produce national, not state-specific, data. Forty-two census collection districts (CDs) were selected Australia-wide, with only six CDs selected within each state. The primary objective of this sample selection was to obtain a nationally representative population, not necessarily one representative of each state.

Coyne states that none of the Queensland CDs were in major provincial centres. Of the six Queensland CDs, four were outside Brisbane. From the national sample, 17 of 42 CDs (40.5%) were outside capital cities. As a comparison, 36% of the Australian population lives outside capital cities.2

Regarding selection of CDs, we excluded only those in Statistical Local Areas defined as 100% rural, and those where the Indigenous population made up 10% or more of the overall population.3 This excluded only 5.8% of the total eligible population. If the prevalence of obesity among this group was double the overall prevalence, this would not significantly alter the national rate.

While the smoking rates in AusDiab were lower than reported elsewhere, the prevalence of obesity, hypercholesterolaemia and hypertension were in line with trends in a series of surveys over the past 20 years.4 In an extensive analysis of food consumption between AusDiab and the 1995 National Nutrition Survey, the rates of fruit and vegetable consumption were within 4% between the surveys for those most commonly eaten.

Since our conclusion was that obesity has increased, the possibility of an underestimate only reinforces our message.