Canadians Misrepresenting Weight, Height

Statistics Canada says Canadians are not as tall and thin as they say they are, which is skewing the nation’s obesity rates. The agency said it is rethinking how it calculates its statistics after discovering the degree to which respondents misstate their height and weight.

“We definitely know we have a problem,” Margot Shields, a senior analyst at Statistics Canada, said yesterday. “Researchers and local health units have to be aware that the prevalence of obesity based on self-reported data is an
underestimate.”

Statistics Canada’s major health surveys, the Canadian Community Health Survey and the National Population Health Survey, rely on respondents to provide their weight and height. Researchers then estimate the person’s body mass index (BMI), which is a measure of weight in relation to height. The data is used to determine the population’s obesity rate.

In 2005, 16% of Canadians were obese, based on self-reported figures. But according to data from actual measurements, 24% were obese.

Ms. Shields and her fellow researchers found that males over-reported their height by 1 cm and females by 0.5 cm. Females under-reported their weight by 2.5 kg, and males by 1.8 kg. People who were overweight or obese were more likely to understate their weight, than those of normal weight. “The increasing prevalence of obesity does not seem to have made excess weight more acceptable, and some evidence suggests that the stigma is intensifying,” said the Statistics Canada report released Wednesday. “This may also explain the greater tendency to under-report weight among females, who may feel more pressure to conform to ‘desirable’ standards.”

Also, older Canadians tend to say they were taller than in reality. Ms. Shields said Statistics Canada is working on “correction equations — formulas to provide more accurate estimates — which will be applied to future surveys.”

“If we are underestimating the number of people who are at a particular body mass index, that may in turn underestimate the health care expenditures and indirect costs [such as loss of productivity] to Canadians misrepresenting society,” said Dr. Yoni Freedhoff, medical director at the Bariatric Medical Institute in Ottawa. It is widely known that this bias is associated with self-reported data so obesity researchers prefer measured data.

Ms. Shields said Statistics Canada is diversifying its research. Next year, it plans to release, for the first time, a survey based on fitness tests and skin fold measurements.

The medical community continues to debate the merit of BMI in measuring obesity. Jean Pierre Despres, director of research in cardiology at the Quebec Hearth Institute, says health professionals must look beyond BMI.

“We are getting fatter in every province of the country. Having said that, who among those who are overweight or obese are truly at increased risk of heart disease and diabetes?”