The psychometric properties of the SDQ: a Rasch analysis based on data from the Young-HUNT study

Abstract Background Mental health among adolescents has become an increasing concern in recent years, as more young people report symptoms of anxiety, depression, and behavioural disorders. The Strengths and Difficulties Questionnaire (SDQ) is a brief behavioural screening tool for children and adolescents and is used for both clinical and epidemiological purposes to measure mental health problems. Previous studies of psychometric analysis of SDQ mainly used classical test-theory. The purpose of this study is to assess the psychometric properties of the SDQ in adolescents by using Rasch analysis. Methods This study was based on self-reported cross-sectional data from the Young-Hunt4 study, conducted in 2017-2019. The target group comprised 8066 13-19 years old adolescents. Theoretically, the SDQ reflects five dimensions. The SDQ contains 25 items with three response categories. The analysis focused on local and trait independence, targeting and reliability. In addition, invariance, including differential item functioning (DIF) across genders, age, health and mental health problems, was considered. Preliminary results The analysis detected problems in all five dimensions. While the externalising and internalising subscales could be considered sufficiently unidimensional, this was not valid for the SDQ total score. The SDQ total score and externalising and internalising subscales suffered from bad targeting, and the reliability indexes were lower than recommended. The SDQ is much better targeted at adolescents reporting mental health problems (mean person location of -0.286) compared to the other groups (mean person location of -0.817 and -1,508 for individuals reporting fair and good mental health, respectively). Preliminary conclusions Due to the lack of unidimensionality, it is not statistically justifiable to calculate a total score of the SDQ. Externalising and internalising subscales could be considered sufficiently unidimensional. Key messages • The SDQ has the potential to measure externalising and internalising problems in adolescence. • The SDQ is much better targeted at individuals reporting mental health problems.