Table 1.

BCT mapping to develop interventions to improve participant retention in trials

Intervention 1: Incentives or rewards to improve trial follow-up clinic attendance Target behaviour = follow-up clinic attendance
TDF domains (frequency*)	Linked BCTs (to be taken forward)	Behaviour change objectives	Example quotes to illustrate the beliefs relevant for the TDF domain identified	Possible intervention content
Reinforcement (7/7), Beliefs about consequences (7/7) and Social influences (6/7)	10.1. Material incentive (behaviour) 10.2 Material reward (behaviour) 10.3 Non-specific reward 10.6 Non-specific incentive10.8. Incentive (outcome) 10.10 Reward (outcome) 10.4 Social reward	Inform the participants that a reward (money/vouchers/other valued objects) will be delivered if and only if there has been effort and/or progress in performing the behaviour. Arrange for the delivery of a reward (verbal/non-verbal/money/vouchers/other valued objects) if and only if there has been effort and/or progress in performing the behaviour.	Yes, incentives are always good aren’t they? Like shopping vouchers or cash, or. That was very much appreciated. … it’s like a little voucher to say thank you for participating, and that was good. I think the other thing that would be encouraging as I mentioned before, is when the survey is completed just to have a little note with a few bullet points on about what the findings from the survey were … I… when I returned the questionnaire it would’ve been nice to receive a small note saying, “Thank you Mr X, we’ve received the questionnaire and it’s going to be included as part of the study”, or just a little recognition that the document had been received and it was now going to be processed as part of the study.	Send an email/letter which thanks them for their time to take part in the trial and/or contains a voucher code and instructions on how to claim it.
Intervention 2: Goal setting for improving questionnaire return Target behaviour = questionnaire return
TDF domain (frequency*)	Linked BCTs (to be taken forward)	Behaviour change objectives	Example quotes to illustrate the beliefs relevant for the TDF domain identified	Possible intervention contents
Goals (13/16)	1.1 Goal Setting (behaviour)	Set or agree on a goal defined in terms of behaviour to be achieved	As for the survey they sent me questionnaires through the post, I haven’t done that because I am on family commitments. … It’s probably about middle priority. it’s a job I have to do. In terms of where it fits with what’s going on in my life with the kids, with work, it’s probably not as high up as that but it’s definitely a job I know I have to complete and send back.	Set goals/targets with participants (during consenting process) that all (e.g. six out of six) questionnaires to be returned to complete taking part in a trial.
Intervention 3: Self-monitoring to improve questionnaire return and clinic attendance Target behaviour = follow-up clinic attendance and questionnaire return
TDF domain (frequency*)	Linked BCTs (to be taken forward)	Behaviour change objectives	Example quotes to illustrate the beliefs relevant for the TDF domain identified	Possible intervention contents
Behaviour regulation (clinic attendance 7/7 and questionnaire return 14/16)	2.3. Self-monitoring of behaviour	Establish a method for the participants to monitor and record their behaviours (i.e. attending clinic appointments/returning questionnaires) as part of a behaviour change strategy to reinforce retention behaviour.	I always had it out in a visible place, so it was always on my coffee table. A visual reminder. I tend to use that (iPhone and a calendar) quite a lot as a reminder I always make sure that I’ve got it (date and time of a clinic appointment) in my diary, and I allocate the time.	Give participants a chart/worksheet/trial calendar of all activities (e.g. how many questionnaires to complete and return and by when). Additionally, a sticker (stating the number of activities out of total activities to be completed) could be sent out with the invitation letter to put on the self-monitoring chart once the task is completed.
Intervention 4: Motivational information to improve questionnaire return and clinic attendance Target behaviour = follow-up clinic attendance and questionnaire return
TDF domain (frequency)	Linked BCTs (to be taken forward)	Behaviour change objectives	Example quotes to illustrate the beliefs relevant for the TDF domain identified	Possible intervention contents
Beliefs about consequences, (clinic attendance 7/7 and questionnaire return 15/16)	5.1. Information about health consequences 5.2. Salience of consequences 5.3. Information about social and environment consequences	Provide information (e.g. written, verbal, visual) about health/social/environmental consequences of performing the behaviour. Use methods specifically designed to emphasise the consequences with the aim of making them more memorable (goes beyond informing about consequences)	I suppose it is a benefit if I’m able to help in the study, if my contribution helps in any way then that’s a benefit to me as well, I suppose. Nothing, I suppose. I didn’t think anything would happen [if they didn’t return the questionnaire]. If they don’t do it, they might upset the trials, and just make a loss of money doing the trial.	Persuade participants to complete behaviour by providing information about consequences of performing a trial related behaviour (clinic attendance/questionnaire return) such as if they do/don’t return the questionnaire what impact it might have on the trial progress/findings. Emphasise this information further with the aim of making them unforgettable to participants.

*Frequency relates to the number of participants reporting barriers or enablers within the domain