Table 1 Summary of the main methodological and ethical considerations when designing SWAT in trials involving adults lacking capacity and proposed solutions

Maintaining the integrity of the host trial

Impact on recruitment and retention rates from interventions aimed at improving proxy decision-making is unclear

• Undertake assessment of host trial context to ensure suitability for the SWAT and anticipate issues with embedding the intervention and/or SWAT

• Adopt an exploratory approach to obtaining and analysing recruitment and retention data in host trials

• Record and report factors affecting intervention effectiveness and/or implementation, and impact on the host trial

Identifying a suitable outcome measure

Far smaller amount of methodological research in trials involving adults lacking capacity, therefore less is known about appropriate outcomes and measurement instruments

• Factor in the need for preliminary work to establish relevant outcomes and outcome measurement instruments (including measurement timing)

• Consider whether work is needed to develop or adapt (and validate) outcome measurement instruments prior to SWAT

Unpredictability of sample sizes

SWAT sample size is dependent on the host trials, which may be more heterogeneous and have greater uncertainty than for SWATs in other populations

• Work with the host trial team to assess the likely proportion of participants who will lack capacity (as a whole and by site) and the proportion expected to have a personal consultee/legal representative

• Encourage reporting of capacity status and involvement of consultees/legal representatives in trials involving adults lacking capacity to inform future SWATs

Challenges in consent and data collection

SWAT participant is not generally a participant in the host trial and so does not usually provide their own consent or data for the host trial

• Incorporate flexibility into the design of the SWAT to enable alignment with host trial processes, and so minimise burden for trials and SWAT participants

Uncertainties about the resources needed to deliver the intervention

Trials involving adults lacking capacity are more resource-intensive and so determining the cost of delivering recruitment/retention intervention and conducting a SWAT is particularly important in these trials

• Explore how best to collect resource use data from proxies as non-participants in the host trial and from trial teams

• Work is needed to disentangle the costs of delivering the intervention and SWAT from those needed to deliver the host trial

• Additional work is needed to determine the most appropriate perspective for economic evaluations in these SWATs