Impact of instrument error on the estimated prevalence of overweight and obesity in population-based surveys
- Equal contributors
1 Division of Epidemiology, Norwegian Institute of Public Health, Nydalen, P.O. Box 4404, Oslo, 0403, Norway
2 The Morbid Obesity Centre, Vestfold Hospital Trust, P.O. Box 2168, Tønsberg 3103, Norway
3 Department of Community Medicine, Institute of Health and Society, University of Oslo, Blindern, P.O.Box 1130, Oslo 0318, Norway
4 Laboratory of Anthropogenetics, Vrije Universiteit Brussel, Pleinlaan 2, Brussel 1050, Belgium
5 Department of Public Health, Katholieke Universiteit Leuven, Kapucijnenvoer 35, Leuven 3000, Belgium
BMC Public Health 2013, 13:146 doi:10.1186/1471-2458-13-146Published: 18 February 2013
The basis for this study is the fact that instrument error increases the variance of the distribution of body mass index (BMI). Combined with a defined cut-off value this may impact upon the estimated proportion of overweight and obesity. It is important to ensure high quality surveillance data in order to follow trends of estimated prevalence of overweight and obesity. The purpose of the study was to assess the impact of instrument error, due to uncalibrated scales and stadiometers, on prevalence estimates of overweight and obesity.
Anthropometric measurements from a nationally representative sample were used; the Norwegian Child Growth study (NCG) of 3474 children. Each of the 127 participating schools received a reference weight and a reference length to determine the correction value. Correction value corresponds to instrument error and is the difference between the true value and the measured, uncorrected weight and height at local scales and stadiometers. Simulations were used to determine the expected implications of instrument errors. To systematically investigate this, the coefficient of variation (CV) of instrument error was used in the simulations and was increased successively.
Simulations showed that the estimated prevalence of overweight and obesity increased systematically with the size of instrument error when the mean instrument error was zero. The estimated prevalence was 16.4% with no instrument error and was, on average, overestimated by 0.5 percentage points based on observed variance of instrument error from the NCG-study. Further, the estimated prevalence was 16.7% with 1% CV of instrument error, and increased to 17.8%, 19.5% and 21.6% with 2%, 3% and 4% CV of instrument error, respectively.
Failure to calibrate measuring instruments is likely to lead to overestimation of the prevalence of overweight and obesity in population-based surveys.