Recruitment gets the attention, but a participant who leaves before the primary endpoint costs almost as much as one who was never enrolled. This guide separates why people leave from what a study team can change, and what to track while there is still time to act.
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Enrolled
120
Active
98
Withdrawn
14
Lost to follow-up
8
Longest visit
Key points
Why people leave
It helps to separate the reasons because the remedy depends on which one you are looking at. Teams that lump them under "dropout" tend to reach for reminders in every case.
Long visits, travel, fasting, repeated blood draws, a long daily diary and complicated rules all add up. Attrition from burden shows up as a step down at particular visits. The fix is mostly design: fewer or shorter visits, remote options for procedures that do not need a clinic and a diary that takes a minute on a good day.
People move, change jobs, fall ill, care for a relative or lose their phone. This attrition is steady and looks random. The responses are flexibility (visit windows that fit real lives), several ways to be reached and a clear route to pause rather than withdraw.
Long gaps between contacts, staff turnover, no feedback and a sense that the data go into a void lead to quiet disengagement. Regular, human contact from a named person is the usual remedy, and it costs mostly attention, not money.
Strategies
The evidence for most of these is limited and context-dependent, so decide which to use, state them in the protocol where relevant and watch the data.
| Strategy | What it addresses | How to apply it |
|---|---|---|
| Cut the number and length of visits | Burden | Question every visit and procedure against the endpoints; combine procedures; keep a lean schedule of assessments |
| Allow remote procedures where valid | Burden, travel | Questionnaires and diaries by phone link; home or local sampling where the protocol allows. See home health visits |
| Wide, realistic visit windows | Life | Allow the window the science permits and say so. See visit window calculator |
| Consent that sets honest expectations | Burden, connection | Say how long visits take, what is asked daily and what happens if someone misses a visit. See how to write an eConsent form |
| Collect more than one contact route | Life | Phone, email and an alternative contact the participant allows you to use |
| Named contact person | Connection | One coordinator participants know by name, with a stable way to reach the site |
| Contact between visits | Connection | A short check-in call or message at long gaps, within what the consent allows |
| Early flag for at-risk participants | Life, burden | Missed diary days or a late visit trigger a call, not another automated message |
| Clear withdrawal and pause options | Connection, ethics | A participant who needs a break should know they can ask, and what data continue to be collected |
| Share study progress or results where appropriate | Connection | Newsletter or summary after the study, as approved by the ethics committee |
Payments or incentives, where used, are an ethics committee decision with their own rules on undue influence. Capture does not handle participant payments, so they are handled outside the platform.
Operational support
Retention problems are easiest to fix early, which requires seeing them. In Capture, the study dashboard shows enrolment and visit status by site, and ePRO completion shows who is falling behind on their diary. A coordinator can call a participant after two missed days, not after a missed primary visit.
Site risk
Site 03 needs attention
Action items
2 overdue
What the evidence says
The best-known synthesis is the Cochrane methodology review of strategies to improve retention in randomised trials (Brueton and colleagues, 2013; updated by Gillies and colleagues in 2021). The 2021 update reported that none of the comparisons was supported by high-certainty evidence, that most strategies tested concerned returning postal questionnaires and that few evaluated getting participants back to the site for follow-up. The authors framed their findings as a priority list for replication.
The practical reading: do not promise retention outcomes from a single tactic. Reducing burden is plausible and low-risk, but track your own data. Treat each choice, from visit schedule to follow-up calls, as something to monitor, and describe it honestly in the protocol and in any grant application.
Build the schedule and a diary in the free sandbox, enrol yourself as a test participant and see how heavy the study feels.
A retention plan
List every visit, its length, procedures and travel, and every daily task. Ask what the participant sacrifices for each one.
Remove anything that does not feed a primary or key secondary endpoint. Combine visits where the science allows.
Choose visit windows that fit real life, and record more than one way to reach each participant at enrolment.
For example two missed diary days, a late visit or no response to a call, and who acts on each trigger.
Every month, look at attrition by visit and by site, and write down what you will change if a pattern appears.
There is no single standard. It depends on the condition, the length of the study and the burden. Plan the sample size for expected dropout (see the dropout-adjusted sample size calculator) and set your own targets from similar studies.
Reminders help with forgotten tasks, such as diary entries and visit dates. They do not fix burden or disengagement. Capture sends reminders by email or SMS, but treat them as one tool among several.
No. If your protocol and ethics committee approve payments or incentives, arrange them outside the platform.
A withdrawal is a participant’s decision, recorded with its reason and what data may still be used. Loss to follow-up means contact could not be made after defined attempts. Define the attempts in the protocol and record the outcome for each participant.
Not much. A Cochrane review found no comparison supported by high-certainty evidence. Use burden reduction as a sensible default and monitor your own results.
Yes. Participant status and visit completion are visible by site in the study dashboard, so you can look at attrition by visit.
It should describe what is asked of participants, including visit length, diary tasks, reminders and contact between visits, so there are no surprises. The ethics committee approves the wording.
Keep exploring
Patient recruitment playbook for small trials
The other half of enrolment.
ePRO compliance and diary completion
Keep diaries complete.
ePRO reminders by SMS and email
The reminder ladder.
Dropout-adjusted sample size
Plan for attrition.
Decentralized clinical trial guide
Reduce travel burden.
Home health visits in trials
Visits that come to the participant.
QR code participant enrolment
Low-friction onboarding.
Free sandbox with every feature. No credit card, and you pay only when you go live with real participants.