Measurement Equivalence and Convergent Validity of a Mental Health Rating Scale

Emotional and behavioral problems among children and adolescents may be studied using the Strengths and Difficulties Questionnaire, containing five subscales, based on ratings by parents, teachers, or adolescents themselves. We investigate two measurement issues using data from a longitudinal sample of 8,806 participants aged 7 to 9 years and 11 to 13 years from the Bergen Child Study in Bergen, Norway. First, convergent validity of parent and teacher ratings is studied using a multitrait-multimethod approach. Second, longitudinal measurement equivalence is studied using confirmatory factor analysis, which requires us to deal with the considerable attrition. The multitrait-multimethod indicates not only good convergent validity but also considerable method variance for parents and teachers. The reliability and validity of some subscales are relatively low. Attrition analysis indicates that attrition is not missing completely at random, but estimation assuming missing at random makes no real difference. We conclude that assuming missing completely at random is acceptable. Comparing ratings by parents and teachers results in partial scalar equivalence. In addition, all subscales exhibit (partial) longitudinal scalar measurement equivalence. We recommend using latent variable modeling and not summated scales for longitudinal modeling using the Strengths and Difficulties Questionnaire.