As opposed to a blinded placebo-controlled design, participants receive information based on the open trial design.
Randomising participants at recruitment to an open rather than a blinded trial may result in a large increase in retention.
An increase of 13% (95% confidence interval = 4% to 22%).
GRADE Low certainty.
We recommend that trialists consider using an open trial design where possible.
See Resource bundle below for details on how to use an open trial design.
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 open trial design. The chart below shows the impact of an absolute increase of 13% (95% CI = 4% to 22%). Retention is now 78%, which means our best estimate is that you would now only be 2 responses short.