Statistical analysis
depression, anxiety
REGRESSION, SECONDARY, SENSITIVITY
The trial was designed to detect a standardised mean difference (SMD) between trial arms of 0.4 in HADS total score at 4-months follow-up with 90% power, where 0.4 is in the middle of the range of effect sizes reported for other forms of psychological interventions for depression [Analysis was conducted in accordance with a prespecified analysis plan detailing the analytical models, primary and secondary outcomes, choice of covariates, sensitivity analyses, and all other key aspects of the analysis. The plan was finalised and approved by the Trial Steering Committee prior to data analysis or unmasking. The primary analyses used intention-to-treat principles. For each of the continuous outcomes, a linear mixed effects regression model was applied incorporating both time points (baseline, 4 months). Prespecified covariates in the model were the design stratification actors of hospital site and sex, plus age and medication for depression or anxiety (never taken/currently taking/taken in the past). All other potential covariates (To aid interpretation, we computed effect sizes in the form of SMDs between groups. For consistency with Cochrane reviews and to enable cross-study comparisons, these were computed as the adjusted mean difference between groups from the mixed effects model divided by the pooled standard deviation of change scores from baseline [Being based on statistically significant change within an individual, the RCI can be conservative. We therefore conducted an equivalent analysis based on a published minimal clinically important difference (MCID) for the HADS anxiety and depression subscales of 2 points [We observed a higher attrition rate by 4-months follow-up in the MCT+CR arm. Sensitivity analysis based on MI assumes data is missing at random, which is unlikely in this case. We therefore conducted 2 additional sensitivity analyses to account for differential attrition. The first assumed that patients who dropped-out experienced no change in their outcome scores between baseline and 4 months (a last observation carried forward (LOCF) analysis). The second sensitivity computed the mean 4-month score required among drop-outs to reduce the treatment effect between arms to zero, for each outcome. This score was expressed as a percentile of the outcome’s score distribution among controls at 4 months to aid interpretation. Analyses were conducted using Stata version 14.