Alongside with the follow-up questionnaire, participants receive a voucher or some cash.
Monetary incentives may increase retention.
An increase of 7% (95% confidence interval = 4% to 11%).
GRADE Low certainty.
We recommend that trialists consider using monetary incentives along with the reminder questionnaire.
See Resource bundle below for details on how to implement financial incentives.
Imagine initial retention is 65% of those approached. You have a trial with 100 participants that needs responses from 80 to meet its statistical power calculations. Retention of 65% means that you will be 15 responses short (see chart below).
Now imagine using financial incentives. The chart below shows the impact of an absolute increase of 7% (95% CI = 4% to 11%). Retention is now 72%, which means our best estimate is that you would now only be 8 responses short.