An international scoring system for self-reported health complaints in adolescents.

BACKGROUND Aimed to develop a unitary scoring system for the 'Health Behaviour in school-aged Children' (HBSC) symptom checklist that would facilitate cross-national comparisons and interpretation. Rasch measurement analysis and investigation of differential item functioning (DIF) were conducted. METHODS Data were obtained from the 'WHO collaborative study HBSC 2001/2002'. A total of 162,305 students aged 11, 13 and 15 years from 35 European and North American Countries were surveyed. Unidimensionality of the items and local independence were tested using means of confirmatory factor analysis. DIF across countries, age groups and gender was investigated using a logistic regression procedure. Item and person parameters were estimated according to the Rating Scale Model (RSM). RESULTS All items proved to be unidimensional. One item displayed noticeable DIF across countries and was discarded. The remaining items were functioning equally across subgroups. The RSM analysis resulted in Rasch model conform item parameter estimation. Infit mean square values between 0.84 and 1.35 revealed acceptable item fit. CONCLUSION The control of DIF enables comparable and unbiased assessment of subjective health complaints across countries, age groups and gender. A scoring algorithm could be developed which enables a cross-cultural comparable and interval-scaled assessment of subjective health complaints.