Ravens-Sieberer U, Kurth BM; KiGGS study group, BELLA study group (2009): The mental health module (BELLA study) within the German Health Interview and Examination Survey of Children and Adolescents (KiGGS): study design and methods
Eur. Child Adolesc. Psychiatry 17 (suppl. 1): 10-21.

The BELLA study on mental health and well-being in children and adolescents is the mental health module of the German Health Interview and Examination Survey for Children and Adolescents (KiGGS). The cross-sectional KiGGS survey collected comprehensive data on the health status of 17,641 children and adolescents, aged 0-17 years, living in Germany. The survey included physical examinations and tests, questionnaires filled in by parents and equivalent questionnaires for children aged 11 years or older. A computer-assisted personal interview was conducted by study physicians, and various laboratory tests, e.g. on blood and urine samples, were performed. The longitudinal BELLA study collected initial cross-sectional data from a representative KiGGS sub-sample of families with children aged 7-17 years. Of the 4,199 randomly selected families invited to participate in the BELLA study, 2,863 took part. A total of 48.5% of the participating children and adolescents were girls, 51.5% were boys. Within the BELLA study, trained interviewers conducted standardised telephone interviews with one parent and also the child, if it was at least 11 years old. Afterwards the families received additional questionnaires. The interviews and questionnaires included various standardised and ICD-10-oriented instruments examining overall mental health problems and associated burden, depression, anxiety, attention deficit-/hyperactivity and conduct disorders. Furthermore they covered a broad spectrum of aspects related to mental health and well-being, such as risk and protective factors and health-related quality of life. An analysis of the non-responders showed that the families who agreed to participate form a representative sample with respect to the German population. The sample deviated only slightly from the KiGGS sample structure regarding socioeconomic status and regarding parent-reported mental health problems. No such difference was observed for the children's self-reported mental health. A weighting procedure was applied to correct for deviations from the sociodemographic and socioeconomic structure of the target population.