Measurement invariance of the parent-reported Strengths and Difficulties Questionnaire in autistic adolescents

Mental health conditions are more prevalent in autistic people than non-autistic people. The Strengths and Difficulties Questionnaire is a commonly used screening tool for emotional and behavioural difficulties in autistic children and adolescents. However, few studies have assessed the psychometric properties of the Strengths and Difficulties Questionnaire in populations of autistic people, especially measurement invariance, to examine whether the underlying latent structure is consistent across time or groups. Measurement invariance of the parent-reported Strengths and Difficulties Questionnaire in a nationally representative cohort study was examined: longitudinal invariance (autistic 11-, 14- and 17-year-olds) and group invariance (autistic and non-autistic 17-year-olds). Differential item functioning was explored in the autistic/non-autistic group analysis. The five-factor structure showed inadequate fit, especially in the autistic group; by extension, measurement invariance could not be established. Differential item functioning was observed for several conduct problems, prosocial behaviour and peer problems subscale items, as well as reverse-coded items. Poor structural validity and item-level invariance may confound findings from research within and between populations of autistic and non-autistic adolescents, as well as screening of mental health conditions in autistic adolescents. This research calls for the development and improvement of screening tools for emotional and behavioural difficulties in populations of autistic people while accounting for their heterogeneity.Lay abstract Autistic people are more likely than non-autistic people to experience mental health difficulties. The Strengths and Difficulties Questionnaire is often used to screen for these difficulties and to otherwise make important decisions about mental health treatment and research in populations of autistic people. However, this study suggests that parent-reported Strengths and Difficulties Questionnaire scores may not be useful for comparing autistic and non-autistic adolescents at 11, 14 and 17 years old, as well as screening for mental health conditions in autistic adolescents. In addition, several items may be more likely to be endorsed by parents of autistic 17-year-olds than by parents of non-autistic 17-year-olds (and vice versa), which might suggest caution is needed when comparing groups on specific items.