2.2. Sample Size
Power calculations were performed for the primary outcome variable, i.e., the between-groups magnitude of the change in Raven’s Coloured Progressive Matrices (RCPM). This showed that to provide α = 5% and β = 0.80, a total sample size of 210 was necessary to detect a change of 2.1 between the groups, with a projected standard deviation of 4.1, accounting for the loss to follow-up rate of 20%.