CORRECTION OF THE SELF-REPORTED BMI IN A TEENAGE POPULATION

OBJECTIVE: To investigate the issue of systematic bias in self-reporte d weight and height, and produce a simple procedure which can be used to correct reporting bias. DESIGN: Cross-sectional, with self-reported questionnaires. SUBJECTS: A sub-sample (n = 143) of secondary school students in Siena, Italy, taken from the Food Behaviour Survey (sample size, n = 779). RESULTS: In the teenage sub-sample, both males and fe males under-reported their weight and over-reported their height, such that underestimation of the overweight prevalence was in the order of about 8% for both genders. For both weight and height, the correlatio ns between self-reported and measured values were over 0.90. Conversio n factors were derived to correct the reported body mass index (BMI) d istribution by adjusting the percentages of erroneously classified sub jects in the four BMI categories. CONCLUSION: High correlation coeffic ients (r greater than or equal to 0.75), showing a systematic tendency for erroneous self-reporting of a 'slim-body shape', justify the use of conversion factors (measured/self-reported) to correct BMI distribu tions calculated from self-reported values.