Summary of review finding	Studies contributing to the review finding	Methodological limitations	Coherence	Relevance		Adequacy	CERQual assessment of confidence in the evidence	Explanation of CERQual assessment
Finding 6: Potential participants consider participation disruptive and a burden when additional appointments or travel, or both are needed. Perceived time commitment as a result of trial participation was also identified as a concern for potential participants	Canvin 2006, Harrop 2016a, Costenbader 2007, Habersack 2013, Bleidorn 2015, Attwood 2016, Hughes‐Morley 2016, Normansell 2016, Ballantyne 2017	Minor concerns based on the assessment of six studies with no, two studies with minor and one study with moderate methodological limitations	No or very minor concerns		Minor concerns regarding relevance as studies had limited geographical spread Included a range of medical/surgical, oncology, mental health, pregnancy and childbirth, and health promotion trials. Participants included both acceptors and decliners.	No or very minor concerns	High confidence	No or very minor concerns regarding adequacy and coherence, minor concerns regarding relevance and methodological limitations
Finding 7: A financial benefit in terms of an incentive or reimbursement may not be an overly influencing factor for potential participants. However, it is viewed as a welcome acknowledgement of participants’ time and effort. Other incentives that may be welcome include additional health checks or medications that potential participants may otherwise not be able to afford	Chang 2004, Costenbader 2007, Wasan 2009, Tarimo 2010, Bleidorn 2015, Blodt 2016, Chin 2016, de Lacey 2017	Minor concerns based on the assessment of five studies with no, two studies with minor and one study with moderate methodological limitations	Minor concerns		Moderate concerns regarding relevance as studies had limited geographical spread Included mainly medical/surgical, with one pregnancy and childbirth, and one health promotion trial. Participants included mainly acceptors with only one study including decliners.	No or very minor concerns	Moderate confidence	No or very minor concerns regarding adequacy, minor concerns regarding coherence and methodological limitations, and moderate concerns regarding relevance
Finding 8: Potential participants’ perceptions of randomisation and freedom to withdraw from the trial were important factors in their decision whether to participate in a trial. This was particularly important if they did not fully understand the concept of randomisation or if they had a treatment preference	Canvin 2006, Madsen 2007a, Madsen 2007b, Taylor 2007, Jackson 2010, Moynihan 2012, Smyth 2011, Gopinath 2013, Bleidorn 2015, Oud‐Rengerink 2015, Abhyankar 2016, Bidad 2016, Harrop 2016a, Hughes‐Morley 2016, Normansell 2016, Ballantyne 2017, Sawyer 2017, Dellson 2018	Minor concerns based on the assessment of thirteen studies with no, three studies with minor and one study with moderate methodological limitations	No or very minor concerns		Minor concerns regarding relevance as studies had moderate geographical spread Included a range of medical/surgical, oncology, mental health, pregnancy and childbirth, and health promotion trials. Participants included both acceptors and decliners.	No or very minor concerns	High confidence	No or very minor concerns regarding adequacy and coherence, minor concerns regarding relevance and methodological limitations