Factor structure of the SDQ and longitudinal associations from pre-school to pre-teen in New Zealand

Objective: The objective of this study was to assess the validity of the Strengths and Difficulties Questionnaire in a cohort of New Zealand children followed from birth to the age of eleven. The study also aimed to assess the stability of the child data in relation to behavioural outcomes during this period. Methods: Children in the Auckland Birthweight Collaborative Study were assessed at approximately 3½, 7 and 11 years of age. At all time-points parents completed the parent version of the Strengths and Difficulties Questionnaire, and the children themselves completed the self-report version at 11 years of age. The validity and internal consistency were assessed using exploratory factor analysis, Cronbach’s alpha, and McDonald’s Omega. Cross tabulations and Chi-square statistics were used to determine whether Total Difficulty scores, as per accepted cut-offs, remained stable over time (between normal and abnormal/borderline categories). Results: The factor structure remained relatively consistent across all three time-points, though several questions did not load as per the originally published factor analysis at the earliest age. The internal consistency of the Strengths and Difficulties Questionnaire was good at all time-points and for parent- and child-completed versions. There was low agreement in the total scores between time points. Conclusions: The factor analysis shows that the Strengths and Difficulties Questionnaire has a similar factor structure, particularly in older ages, to that previously published and shows good internal consistency. At the pre-school follow up, a larger than expected proportion of children were identified with high scores, particularly in the conduct sub-scale. Children’s behaviour changes over time, with only poor to moderate agreement between those identified as abnormal or borderline over the longitudinal follow up.