Recruitment and Retention

RCTs must recruit an adequate number of appropriate participants. Then they must retain as many of those participants as possible, for the time period specified in the study protocol. Recruitment and retention are challenges that involve much time and effort on the part of both clinicians and researchers.

Please see this linked document to find out more about how we manage randomisation, at Keele CTU.
If you would like further information on randomisation, please drop the team an email at


It takes a lot of work to recruit participants to a trial. It is really important that the trial design makes recruitment as straightforward as possible. If the design is too complex, sites will struggle to identify patients suitable for the trial and if participating is too time consuming or restrictive, participants will not agree to take part. Many trials will include a pilot phase to test recruitment processes or to conduct qualitative work, to gain feedback from participants and staff on the study processes.

For successful recruitment, it is really important to maintain good communication with site staff and with potential participants, through newsletters, blogs, website materials and other online methods. Visit the NIHR website to learn how patient engagement can improve recruitment and retention.

Participant Information

Before a participant is recruited into a study they should (where possible) fully understand what taking part will involve. They should have time to consider trial information carefully and discuss taking part with their family and friends. Usually, this information will be described using a participant information sheet which will clearly explain to participants what will happen if they choose to take part and should include information on:
• Pathway through the study
• Study interventions
• Randomisation procedures
• Potential risks and benefits
• Data management and storage
• Study withdrawal process
• Ethical approval and funding bodies
• Details of an independent body for complaints
• Study team details and contact numbers

As well as the participant information sheet (PIS), information can be shared by; letters, posters or through media campaigns. The information needs to take account of the age group of participants e.g. short clear information with images should be used to help explain a study to children. Plain English, jargon-free information is essential! All patient-facing documentation must have ethical approval. Click here for an example from one of our studies.


In most trials (where the participant is able to do so) and after considering the information about the trial the potential participant will be asked to provide informed consent, usually by signing a consent form. For the consent to be valid, it must be voluntary and informed, and the person consenting must have the capacity to make the decision.

The HRA provide guidance on consent and a template consent form.

All those consenting to take part in a trial are free to withdraw at any time and without giving a reason.

At Keele CTU all consent forms are stored securely and separately to participant data. Consent forms will also be retained by the sites where the consent is taken. These forms are retained for the entire trial period and archived as they are key trial documents.

Having recruited a participant into a trial it is critical for the successful outcome of the trial to retain them throughout their treatment and follow up period. That follow up might involve collecting information from participants for many months or even several years.

Participants can be lost from the trial follow up for many reasons; they may move address, or lose interest in the trial. They may be too busy or their health may prevent them from continuing. They may find the treatment not to their liking or find completing questionnaires too time-consuming.

It is really important that participants understand all that is involved throughout the trial before they take part. It is also important to make follow up as straight forward as possible and to use methods to keep in touch between follow up visits or data collection periods.

Keele CTU use lots of methods to retain our participants, including using SMS for straightforward data collection and visit reminders. We offer a choice on how follow up data is collected (by post or phone, online or by SMS) and we send reminders and newsletters to keep in touch with our participants.