Background: The German Health Interview and Examination Survey for Children and Adolescents (KiGGS) is an important data source for assessing the occurrence of underweight, overweight and obesity in children and adolescents in Germany. However, to assess trends over time, it must be considered that methodological changes in the calculation of prevalences have been necessary and that the reference system has been revised.
Objective: Are the effects of the methodological changes in weighting factors and reference systems so important that they significantly influence the available prevalence estimates and statements on trends over time?
Materials and methods: The data are based on valid measurements of body height and weight from the KiGGS baseline survey (2003-2006, 7531 boys and 7215 girls) and from KiGGS Wave 2 (2014-2017, 1762 boys and 1799 girls). The participants were aged between 3 and 17 years. Prevalences (%, 95% CI) of underweight, overweight and obesity for the KiGGS baseline survey were calculated depending on the reference system and different weighting factors used.
Results: The statements on the temporal trend in the prevalence of underweight, overweight, and obesity remain valid even when methodological changes are taken into account. Only among 16- and especially 17-year-old girls, can a noticeable difference due to the altered reference system be noted.
Discussion: With regard to the trend examined here, the methodological changes can be neglected, as long as no small subgroups are analysed. However, this conclusion cannot be generalised; the effects of methodological changes must be re-examined for each study question.
Keywords: Children and adolescents; Overweight and obesity; Reference system; Survey weighting; Underweight.