Monaz: Hello, I'm Monaz Mehta, editor in the Cochrane Editorial and Methods department. One of the most used Cochrane Methodology Reviews looks at the effects of interventions intended to boost recruitment to randomised trials. In October 2020, this was supplemented by a qualitative evidence synthesis of factors that impact on a person's decision to join a trial. We asked the lead author, Catherine Houghton from the National University of Galway in Ireland to outline the findings.

Catherine: Recruiting trial participants is challenging and the reasons why people agree or decline to participate are complex, but not recruiting enough people into a trial can lead to research waste. Learning more about what influences this decision can provide guidance for better recruitment strategies and, to help with this, we used a qualitative evidence synthesis approach to identify factors that impact on a person's decision to take part in a randomised trial. 
We found 86 studies and sampled 29 of these for analysis. Just over half the studies were done in the UK, but there were also six from other European countries, three from the USA and one each from Australia, Canada, New Zealand and Tanzania.
The trials that potential participants were invited to join covered a broad range of health areas. These include cancer, pregnancy and childbirth, mental health and health promotion; and a variety of interventions were being tested, including different types of surgery, psychological therapies, vaccinations and pharmaceutical treatments. The approaches to recruitment in the studies also varied with, for example, some using face‐to‐face invitations during a regular consultation with a healthcare professional or during a special session with research staff, invitation letters or phone calls, and posters or leaflets.
We found several important factors that influenced the decision to join a randomised trial. In general, people preferred to be invited face‐to‐face, with information communicated clearly, and written information was also useful. The timing of the invitation is important, because potential participants could find it difficult to differentiate between the care they would usually receive and that which would be provided as part of the trial. They may also be coming to terms with a diagnosis, which can impact on their decision.
The level of commitment to the trial worried some people. Some believed that extra appointments and the time involved would be a burden; and, although some welcomed payment to compensate them for this, this was not seen as a very important factor that influenced their decision. 
The person's perception of their own health was another factor. For instance, if someone feels healthy, they may worry about risking their health by taking part in a trial and, if someone feels unwell, they may not want to risk making this worse. On the other hand, someone who is healthy or very ill may feel they have “nothing to lose” by taking part in the trial. So, it is not just about how healthy someone is but rather how they feel about their health.
Also, what the person's doctor or nurse says may influence their decision, as can something said by family, friends or in the media. Finally, the possible benefits of taking part in the trial are key to the decision. Individuals are influenced by the chance of improvement to their health; the chance to feel better if the therapy or treatment works. Also, many welcome the opportunity to participate for reasons of altruism or to make a difference by contributing to science. 
To conclude, we have moderate to high level confidence in our findings and from them, we've developed key questions that can help researchers to consider how to recruit people into trials. These insights should influence or underpin future recruitment strategies, so that these are developed in a participant‐driven way, that ultimately improves trial conduct and reduces research waste.

Monaz: If you'd like to see the questions that Catherine mentioned and explore the research they reviewed in more depth, you can find the full qualitative synthesis at Cochrane Library dot com with a search for 'qualitative evidence for recruitment to trials'.