Challenges in the design, planning and implementation of trials evaluating group interventions.

backgroundGroup interventions are interventions delivered to groups of people rather than to individuals and are used in healthcare for mental health recovery, behaviour change, peer support, self-management and/or health education. Evaluating group interventions in randomised controlled trials (RCTs) presents trialists with a set of practical problems, which are not present in RCTs of one-to-one interventions and which may not be immediately obvious.

methodsCase-based approach summarising Sheffield trials unit's experience in the design and implementation of five group interventions. We reviewed participant recruitment and attrition, facilitator training and attrition, attendance at the group sessions, group size and fidelity aspects across five RCTs.

resultsMedian recruitment across the five trials was 3.2 (range 1.7-21.0) participants per site per month. Group intervention trials involve a delay in starting the intervention for some participants, until sufficient numbers are available to start a group. There was no evidence that the timing of consent, relative to randomisation, affected post-randomisation attrition which was a matter of concern for all trial teams. Group facilitator attrition was common in studies where facilitators were employed by the health system rather than the by the grant holder and led to the early closure of one trial; research sites responded by training 'back-up' and new facilitators. Trials specified that participants had to attend a median of 62.5% (range 16.7%-80%) of sessions, in order to receive a 'therapeutic dose'; a median of 76.7% (range 42.9%-97.8%) received a therapeutic dose. Across the five trials, 75.3% of all sessions went ahead without the pre-specified ideal group size. A variety of methods were used to assess the fidelity of group interventions at a group and individual level across the five trials.

conclusionThis is the first paper to provide an empirical basis for planning group intervention trials. Investigators should expect delays/difficulties in recruiting groups of the optimal size, plan for both facilitator and participant attrition, and consider how group attendance and group size affects treatment fidelity.

trial registrationISRCTN17993825 registered on 11/10/2016, ISRCTN28645428 registered on 11/04/2012, ISRCTN61215213 registered on 11/05/2011, ISRCTN67209155 registered on 22/03/2012, ISRCTN19447796 registered on 20/03/2014.