Statistical Analysis
REGRESSION, SECONDARY
The power calculation, following methods outlined by Hemming et al,Study groups remained masked until exploratory analyses were completed. Missing items in the SDQ and GHQ were addressed using methods described for the scales.Analyses were conducted in 3 stages: (1) effect of intervention on change in SDQ scores from baseline to the 3- and 6-month follow-ups; (2) effects of intervention on secondary outcomes, including receipt of mental health care during the study, change in parental mental health, and parent and GP reports of care at the index visit; and (3) planned subgroup analyses corresponding to GP characteristics. We additionally explored possible heterogeneity related to parent and child characteristics (child age, child gender, and parent GHQ status).As planned, we initially used multilevel regression (child or parent observations clustered within GPs) with the interaction of time (as a categorical variable) and GP group assignment as a predictor of child or parent outcomes.