Long-Term Outcome of a Cluster-Randomized Universal Prevention Trial Targeting Anxiety and Depression in School...

The present study concerns a 3-year follow-up of a universal prevention trial targeting anxiety and depressive symptoms in school children. In addition to evaluating the long-term effect of the prevention program, we also examined attrition and its effect on the outcome. High rates of attrition have commonly been observed in studies in the field. However, the role of attrition is not sufficiently understood regarding internal and external validity biases. The current study comprised 695 children (aged 8-11 at baseline) from 17 schools in Sweden. Schools were cluster-randomized to either the intervention or control condition. Children completed measures of anxiety and depressive symptoms and parents completed measures of their child's anxiety and general mental health. We found no evidence of long-term effects of the prevention program, except for a small effect regarding parent reports of child anxiety. However, that effect was not found to be of clinical significance. Regarding attrition, children with missing data at the 3-year follow-up displayed higher levels of psychiatric symptoms at baseline and increasing symptoms across time. Furthermore, children in the control condition with missing follow-up data were found to be significantly deteriorated across time compared to the corresponding children in the intervention condition regarding depressive symptoms and total difficulties. In other words, attrition served as a moderator of the effect, which suggests that the overall result was biased toward a null-result. Our study highlights that large and nonrandom attrition severely limits the validity of the results. Further, given the common problem of retaining participants in long-term evaluations of school-based prevention trials, previous studies may suffer from the same limitations as the current study.