The KiGGS survey is based on a nationally representative sample of children and adolescents 0–17 years of age with main residence in Germany. The sampling procedure was based on a two-stage protocol developed in co-operation with the Centre for Survey Research and Methodology (ZUMA), Mannheim, Germany. The study was approved by the Charité/Universitätsmedizin Berlin ethics committee and the Federal Office for the Protection of Data.
First, a systematic sample of 167 primary sample units (PSUs) was drawn from an inventory of German communities stratified according to the BIK classification system [2 ], which measures the grade of urbanization, and the geographic distribution. The number of PSUs per strata was determined using the Cox procedure for community sampling [3 (link)] with sampling probability proportional to population size. In order to ensure sufficient sample size for analyses stratifying according to residence in former East or West Germany, a disproportionate number of PSUs was included to represent former West (n = 112) and East (n = 50) Germany, and the city of Berlin (n = 5). At the second stage, an equal number of addresses (n = 24) per birth cohort were randomly selected (simple random sample) from local population registries within selected PSUs 8 weeks prior to the start of examinations. A final simple random sample was drawn at the Robert Koch Institute, including a total of 8, 9 or 10 children and adolescents per birth cohort, depending on community size. Thus, the target population per PSU consisted of 144, 162 or 180 persons eligible to be contacted and invited to participate in the study. Oversampling of children and adolescents from families with a migration nationality was used, as we expected a higher proportion of undeliverable contacts and non-respondents in this subgroup compared to children and youths from non-migrant families. The total KiGGS sample included 28,299 children and adolescents.
First, a systematic sample of 167 primary sample units (PSUs) was drawn from an inventory of German communities stratified according to the BIK classification system [2 ], which measures the grade of urbanization, and the geographic distribution. The number of PSUs per strata was determined using the Cox procedure for community sampling [3 (link)] with sampling probability proportional to population size. In order to ensure sufficient sample size for analyses stratifying according to residence in former East or West Germany, a disproportionate number of PSUs was included to represent former West (n = 112) and East (n = 50) Germany, and the city of Berlin (n = 5). At the second stage, an equal number of addresses (n = 24) per birth cohort were randomly selected (simple random sample) from local population registries within selected PSUs 8 weeks prior to the start of examinations. A final simple random sample was drawn at the Robert Koch Institute, including a total of 8, 9 or 10 children and adolescents per birth cohort, depending on community size. Thus, the target population per PSU consisted of 144, 162 or 180 persons eligible to be contacted and invited to participate in the study. Oversampling of children and adolescents from families with a migration nationality was used, as we expected a higher proportion of undeliverable contacts and non-respondents in this subgroup compared to children and youths from non-migrant families. The total KiGGS sample included 28,299 children and adolescents.
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