WE'RE fatter than we think. A research paper released yesterday by the Bureau of Statistics calls into question the data commonly used to measure obesity in the Australian population because survey respondents tend to describe themselves as taller and lighter than they actually are.

''On average, respondents overestimate their height and underestimate their weight,'' the report says. This throws out the measure of body mass index (BMI), a commonly used indicator of a person's general health and their risk of diseases including diabetes and heart disease.

Both women and men underestimated their weight and overestimated their height. Credit:John Woudstra

Researchers Tim Ayre, Jason Wong and Anil Kumar compared results from surveys taken in 1995 and in 2007-08 and found consistent trends in both.

In both studies, respondents were asked to approximate their height and weight and then given the option of having their actual height and weight measured. Both men and women tended to overestimate their height, though women were particularly guilty of underestimating their weight.