Impact of a waitlist comparator design on recruitment, retention and outcomes in open-label parallel-group randomised trials

1. To assess whether a randomised trial with a waitlist comparator arm increases recruitment compared to a trial without a waitlist comparator arm.
2. To assess whether a randomised trial with a waitlist comparator arm increases retention compared to an trial without a waitlist comparator arm.
3. To assess whether participants in a randomised trial who are allocated to a comparator arm report different levels of activity comprising “usual care” depending on whether or not the
comparator includes a waitlist.
4. To assess whether participants in a randomised trial who are allocated to a comparator arm report different outcomes depending on whether or not the comparator includes a waitlist.