Abstract
BackgroundBased on successive Health Interview Surveys (HIS), it has been demonstrated that also in Belgium obesity, measured by means of a self-reported body mass index (BMI in kg/m2), is a growing public health problem that needs to be monitored as accurately as possible. Studies have shown that a self-reported BMI can be biased. Consequently, if the aim is to rely on a self-reported BMI, adjustment is recommended. Data on measured and self-reported BMI, derived from the Belgian Food Consumption Survey (FCS) 2014 offers the opportunity to do so.MethodsThe HIS and FCS are cross-sectional surveys based on representative population samples. This study focused on adults aged 18–64 years (sample HIS = 6545 and FCS = 1213). Measured and self-reported BMI collected in FCS were used to assess possible misreporting. Using FCS data, correction factors (measured BMI/self-reported BMI) were calculated in function of a combination of background variables (region, gender, educational level and age group). Individual self-reported BMI of the HIS 2013 were then multiplied with the corresponding correction factors to produce a corrected BMI-classification.ResultsWhen compared with the measured BMI, the self-reported BMI in the FCS was underestimated (mean 0.97 kg/m2). 28% of the obese people underestimated their BMI. After applying the correction factors, the prevalence of obesity based on HIS data significantly increased (from 13% based on the original HIS data to 17% based on the corrected HIS data) and approximated the measured one derived from the FCS data.ConclusionsSince self-reported calculations of BMI are underestimated, it is recommended to adjust them to obtain accurate estimates which are important for decision making.
Highlights
Based on successive Health Interview Surveys (HIS), it has been demonstrated that in Belgium obesity, measured by means of a self-reported body mass index (BMI in kg/m2), is a growing public health problem that needs to be monitored as accurately as possible
Survey methodology This study focused on adults aged 18–64 years, since the Food Consumption Survey (FCS) targeted the Belgian population of 3–64 years and the relative weight of children and youngsters is not yet stable [26]
The educational level is based on the International Standard Classification of Education (ISCED) whereby the low educated people have at most a higher secondary education and the high educated people at least a post-secondary or tertiary education
Summary
Based on successive Health Interview Surveys (HIS), it has been demonstrated that in Belgium obesity, measured by means of a self-reported body mass index (BMI in kg/m2), is a growing public health problem that needs to be monitored as accurately as possible. The BMI calculated in the HIS is based on selfreported height and weight collected by means of a questionnaire Such an approach is commonly used in large epidemiological studies [9,10,11,12] because collecting self-reported data is more feasible and less expensive than collecting objective measurements [2, 13,14,15]. This was expressed in terms of the absolute difference, calculated as the mean measured BMI minus the mean self-reported BMI (negative in case of over-reporting and positive in case of under-reporting), and in terms of the relative difference, calculated as the mean measured BMI divided by the mean self-reported BMI These calculations were stratified by the combination of four background variables: region (3) * gender (2) * educational level (2) * age group (3), resulting in 36 strata
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