Body mass index: comparing mean values and prevalence rates from telephone and examination surveys.
BACKGROUND
Cost effective means of assessing the levels of risk factors in the population have to be defined in order to monitor these factors over time and across populations. This study is aimed at analyzing the difference in population estimates of the mean levels of body mass index (BMI) and the prevalences of overweight, between health examination survey and telephone survey.


METHODS
The study compares the results of two health surveys, one by telephone (N=820) and the other by physical examination (N=1318). The two surveys, based on independent random samples of the population, were carried out over the same period (1992-1993) in the same population (canton of Vaud, Switzerland).


RESULTS
Overall participation rates were 67% and 53% for the health interview survey (HIS) and the health examination survey (HES) respectively. In the HIS, the reporting rate was over 98% for weight and height values. Self-reported weight was on average lower than measured weight, by 2.2 kg in men and 3.5 kg in women, while self-reported height was on average greater than measured height, by 1.2 cm in men and 1.9 cm in women. As a result, in comparison to HES, HIS led to substantially lower mean levels of BMI, and to a reduction of the prevalence rates of obesity (BMI>30 kg/m(2)) by more than a half. These differences are larger for women than for men.


CONCLUSIONS
The two surveys were based on different sampling procedures. However, this difference in design is unlikely to explain the systematic bias observed between self-reported and measured values for height and weight. This bias entails the overall validity of BMI assessment from telephone surveys.
Institute for social and preventive medicine, University of Lausanne, Switzerland Institut universitaire de médecine sociale et preventive, rue du Bugnon 17, CH-1006 Lausanne Switzerland. fred.paccaud@inst.hospvd.ch
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F
Paccaud
V
V
Wietlisbach
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M
Rickenbach
D000328:Adult; D017677:Age Distribution; D000368:Aged; D015982:Bias; D001827:Body Height; D015992:Body Mass Index; D001835:Body Weight; D003625:Data Collection / Q000379:methods / Q000592:standards*; D005260:Female; D006306:Health Surveys; D006801:Humans; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000175:diagnosis* / Q000453:epidemiology*; D010808:Physical Examination / Q000592:standards*; D015995:Prevalence; D012107:Research Design / Q000592:standards; D012494:Sampling Studies; D017678:Sex Distribution; D011795:Surveys and Questionnaires / Q000592:standards*; D013557:Switzerland / Q000453:epidemiology; D013689:Telephone