Table 3 Criteria, measurement and the pass/fail system to determine study feasibility

Recruitment across sites

Successful enrolment and recruitment rates will be monitored. Information will include number of participants recruited, number of participants declining and reasons for declining, and number of participants retained. Establishing a 50% recruitment rate threshold acknowledges the challenges inherent in recruiting individuals with ABI while also ensuring that the resources allocated to the study including time, funding and personnel are maximised. Recruitment rate will be determined as the % of target N recruited. The percentage of patients invited who agree to take part in the intervention will also be calculated

Issues at 1 + sites

All three sites recruit eligible patients

Recruitment rate (%)

< 50%

≥ 50%

Randomisation process

Randomisation process failures are defined as randomising an ineligible patient, a breakdown of the randomisation process and failure to adhere to the randomisation allocation. Maintaining a low threshold for randomisation process failures helps to ensure reliability and validity of trial outcomes

2 + issues with randomising

< 2 issues randomising participants

Intervention compliance (%) — clinicians

Adherence to the treatment manual as assessed by review of a content checklist, completed by the group facilitator at the end of every session at each of the three sites. Setting a threshold of 80% ensures a high standard of intervention fidelity across sites while still accounting for minor deviations that may occur due to contextual factors or facilitator styles

< 80%

≥ 80%

Intervention adherence (%) — participants

Attendance at a minimum of six sessions will be used to measure adherence. Full or partial completion of the two pieces of mandatory homework allocated to participants during session 1 and session 5 will also be documented. Setting the threshold at 75% ensures that participants are engaging in at least six of eight sessions of the intervention while also mindful of potential challenges participants may face such as scheduling conflicts and unexpected circumstances

< 75%

≥ 75%

Data collection

Success would be indicated if completion rates for post-intervention assessment and follow-up data collection reach a satisfactory threshold, taking into account practical considerations including participant compliance and capacity, versus representativeness and generalisability. Missing data will be reported

< 70%

≥ 70%

Attrition rates

Attrition will be calculated as the percentage of participants dropping out of the study relative to the numbers recruited. Reasons for withdrawal and loss to follow-up will be reported. Setting an attrition threshold at 40% acknowledges the potential challenges of participant retention in longitudinal studies

≥ 40%

< 40%