Table 1 Variables to be extracted

1. .Protocol title, author and year, source of funding

2. Trial characteristics (disease area, patient population, duration of the follow-up period, number of follow-up assessments, intervention, and comparator)

3. Primary outcome (the primary outcome, whether it is a patient-reported vs non-patient-reported outcome)

4. Planned sample size

5. Mention of using the SPIRIT guidelines in the development of the protocol (“yes” or “no”)

6. Description of retention strategies outlined in the protocol

7. Does the description of the retention strategy include all the information recommended by the SPIRIT guidelines Sect. 18b (“yes” or “no”)

“Plans to promote participant retention and complete follow-up including list of any outcome data to be collected for participants who discontinue or deviate from intervention protocols” (8;3)

8. Mode of follow-up, e.g. questionnaire, clinic visit, telephone call, etc

9. Routine data collection (yes or no)

10. Mention of Patient and Public Involvement (PPI) in relation to retention

11. Mention of cost associated with retention strategy