ABSTRACT
The Positive Psychotherapy for Psychosis intervention was then evaluated in a pilot randomised controlled trial (ISRCTN04199273). The trial protocol was published,12 and full reports of outcome evaluation8 and process evaluation9 from the trial have been published elsewhere. A target sample size of thirty complete data sets in each trial arm was chosen according to recommendations for pilot trials,169 with an anticipated 25 per cent dropout. The obtained sample size allowed effectiveness at a medium effect size (Cohen’s d = 0.5) to be detected with 90 per cent power at a 5 per cent significant level, taking into account 20 per cent attrition.
