27 Because of the uncertainty surrounding the frequency of harms, it is unclear what level of delayed benefit would justify exposing patients to those immediate harms.
340 341 The protocol should describe the procedures for and frequency of harms data collection, the overall surveillance timeframe, any instruments to be used, and their validity and reliability, if known.
We therefore grouped the data for numbers of days with self harm events, creating an ordered categorical variable of frequency of self harm with seven categories defined as none, less than once per month, less than once per fortnight, less than once per week, once or more per week, twice or more per week, and most days.
That depends on the frequency of the harm caused by treatment, and the relative importance of the harm compared to the benefit.
For the primary outcome, we analysed data for 364 patients (group therapy 181, routine care 183) under intention to treat for frequency of self harm and 365 (group therapy 182, routine care 183) for severity of self harm (table 2).
Cost-effectiveness was explored at 12 months in terms of the proportion of young people who had not self harmed over the preceding six months, rather than the categorical primary outcome measure, frequency of self harm.
Randomisation was by minimisation controlling for baseline frequency of self harm, presence of conduct disorder, depressive disorder, and severity of psychosocial stress.
50 Our pilot study 25 suggested that a 50% reduction in the frequency of self harm was possible as a result of the developmental group psychotherapy intervention.
An interim analysis with concealment of the allocation group suggested that the primary outcome measure (frequency of self harm) was very highly skewed.
