Recruitment interventions for trials involving adults lacking capacity to consent: methodological and ethical considerations for designing Studies Within a Trial (SWATs)

Victoria Shepherd* (Corresponding Author), Fiona Wood, Katie Gillies, Abby O'Connell, Adam Martin, Kerenza Hood

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


BACKGROUND: The number of interventions to improve recruitment and retention of participants in trials is rising, with a corresponding growth in randomised Studies Within Trials (SWATs) to evaluate their (cost-)effectiveness. Despite recognised challenges in conducting trials involving adults who lack capacity to consent, until now, no individual-level recruitment interventions have focused on this population. Following the development of a decision aid for family members making non-emergency trial participation decisions on behalf of people with impaired capacity, we have designed a SWAT to evaluate the decision aid in a number of host trials (CONSULT). Unlike in recruitment SWATs to date, the CONSULT intervention is aimed at a 'proxy' decision-maker (a family member) who is not a participant in the host trial and does not receive the trial intervention. This commentary explores the methodological and ethical considerations encountered when designing such SWATs, using the CONSULT SWAT as a case example. Potential solutions to address these issues are also presented.

DISCUSSION: We encountered practical issues around informed consent, data collection, and follow-up which involves linking the intervention receiver (the proxy) with recruitment and retention data from the host trial, as well as issues around randomisation level, resource use, and maintaining the integrity of the host trial. Unless addressed, methodological uncertainty about differential recruitment and heterogeneity between trial populations could potentially limit the scope for drawing robust inferences and harmonising data from different SWAT host trials. Proxy consent is itself ethically complex, and so when conducting a SWAT which aims to disrupt and enhance proxy consent decisions, there are additional ethical issues to be considered.

CONCLUSIONS: Designing a SWAT to evaluate a recruitment intervention for non-emergency trials with adults lacking capacity to consent has raised a number of methodological and ethical considerations. Explicating these challenges, and some potential ways to address them, creates a starting point for discussions about conducting these potentially more challenging SWATs. Increasing the evidence base for the conduct of trials involving adults lacking capacity to consent is intended to improve both the ability to conduct these trials and their quality, and so help build research capacity for this under-served population.
Original languageEnglish
Article number756
Issue number1
Publication statusPublished - 6 Sep 2022


  • Adult
  • Family
  • Humans
  • Informed Consent
  • Proxy
  • Randomized Controlled Trials as Topic
  • Research Design
  • Uncertainty


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