Table 8 Challenges and potential solutions to the implementation of group interventions

Participant recruitment: A number of participants (likely to be a minimum of 8 in each arm to allow for drop out) need to be recruited before a group intervention can commence

Participant recruitment rates can be affected by the relative timing of screening, randomisation and initiation of group, but there is no clear signal as to the best strategy

Recruitment projection and the timing of intervention delivery need to be considered together at the design stage. Those planning group intervention trials should consider demand-forecasting procedures, like those used in clinical settings characterised by surges and slumps and should aim for the maximum group number before commencing the group sessions to allow for attrition.

Consider the pros and cons of randomising patients closer to consent (potentially better for accrual rates) or to group initiation (potentially better for retention rates)

Participant attrition: Attrition may be greater where individuals are required to wait longer before starting the group sessions (due to the requirement of recruiting enough people per group)

Delaying randomisation until there are enough recruited participants to run the group may lead to attrition between consent and randomisation but reduce post-randomisation, pre-intervention attrition, which is important to maintain statistical power

Maintaining contact with participants before randomisation and the setting up of group sessions may help to reduce pre-randomisation attrition

If randomising a number of participants at the same time, trialists should consider and plan for the impact on the follow-up data collection, these participants will need to be followed-up at the same time

Setting group dates: Deciding when to set the group sessions can be challenging. Day/dates can be set before recruitment or once all participants needed for a group session are recruited

Our data did not suggest that either method is superior

Those planning group intervention trials should plan groups around the recruitment projection and allow for some flexibility if recruitment does not go as planned

Facilitator training and attrition: Two facilitators are often needed to run group sessions. Recruiting facilitators can be challenging

Group facilitators will be lost over the course of the intervention delivery – our data show 70% attrition of trained facilitators in one trial

Allow enough time to recruit and train facilitators prior to the start of recruitment

Plan to train replacement facilitators at each site, and/or plan for training sessions throughout the project to account for facilitator attrition or re-training facilitators

Group dynamics are important to group interventions; any change in facilitator should be recorded and investigated as part of the process evaluation and through multi-level modelling for analysis where appropriate

Therapeutic dose: This can be difficult to determine for complex interventions but is required for a per-protocol analysis. This may be more difficult for group interventions, as there is less control over what people are exposed to than in one-to-one sessions

In our experience, investigators define a therapeutic dose by a threshold number of sessions attended

Defining the per-protocol population should be undertaken by expert consensus, with oversight from the project steering committee. Time should be reserved for this purpose during protocol development

For group interventions, ‘therapeutic dose’ may relate to certain intervention criteria being delivered rather than the number of sessions attended and this should be investigated as part of the process evaluation

Group size: An ideal group size will be applicable to the intervention but may be difficult to achieve for all group sessions. Groups may have to run with fewer participants than the ideal. There may be reluctance to amend the group membership (e.g. by adding new participants) once running due to the impact of group dynamics

The impact of group size on the effectiveness of the intervention and must be considered in fidelity assessments and on outcomes

Protocol development should include discussions about what happens in the event of small groups and should specify if any number of participants is too few for intervention delivery. Can groups be combined or can new participants or non-participants be added? Consider whether the group size or the maintenance of group dynamics is more important to the intervention

Process evaluation: Assumes interventions work at an individual level meaning some constructs may need adapting for assessing group interventions

Recruitment and ‘dose delivered’ can be assessed at the group level whereas ‘dose received’ can be assessed at the individual level; fidelity can be assessed at the group (delivery) or individual level (receipt and enactment of skills)

Process evaluations should include components of the intervention specific to group processes, such as facilitation techniques, group dynamics and development and inter-personal change processes

Clustering issues: Couples recruited to trials and participants that receive the same intervention from the same facilitators are likely to have more similar outcomes than if this was not the case. RCTs may not be powered to use multi-level modelling

This needs to be accounted for in the sample size calculation and made clear when interpreting the findings