METHODS: 378 adolescents (M age = 15.5, 68% female) with elevated depressive symptoms were randomized in one of three conditions and were assessed at pretest, posttest, and 6-month follow-up. We tested the moderating effect of three individual (baseline depressive symptoms, negative attributional style, substance use), three environmental (negative life events, parental support, peer support), and two sociodemographic (sex, age) characteristics.
RESULTS: Baseline depressive symptoms interacted with condition and time. Decomposition indicated that elevated baseline depressive symptoms amplified the effect of CB bibliotherapy at posttest (but not 6-month follow-up) relative to the control condition, but did not modify the effect of CB group relative to the control condition or relative to bibliotherapy. Specifically, CB bibliotherapy resulted in lower posttest depressive symptoms than the control condition in individuals with elevated, but not average or low baseline symptoms. We found no interaction effect for other putative moderators.
CONCLUSIONS: Our findings suggest that bibliotherapy is effective only in participants who have elevated depressive symptoms at baseline. The fact that no study variable moderated the effects of CB group, which had a significant main effect in reducing depressive symptoms relative to the control condition, suggests that this indicated prevention intervention is effective for a wide range of adolescents.