The psychometric properties of the self-reported SDQ – An analysis of Swedish data based on the Rasch model

The Strength and Difficulties Questionnaire (SDQ) is increasingly used as a survey instrument for tapping information about mental health problems among children and adolescents. According to most of the evaluations of the SDQ, the instrument shows sound psychometric properties. The purpose of this paper is to analyse the properties of five subscales of the self-reported SDQ by using latent trait theory and the Rasch model, with a focus on the operating characteristics of the items. The analysis is based on cross-sectional data collected in Sweden in 2003 and 2004 among adolescents aged 12–18. In all, six sets of data including 8838 students are used. The analysis detected problems in all dimensions. In particular, the conduct problems scale seemed problematic. By removing misfitting items some improvements were achieved in the post-hoc analysis. However, the ambiguous nature of some items is a major cause for concern but also a potential for improvements of the instrument. It is therefore recommended that each of those items that include two sentences is split into two new items, in order to be tested in forthcoming studies.