Participants receive a self-sampling kit along with a reminder and a leaflet.
Using a self-sampling kit probably increases retention.
An increase of 9% (95% confidence interval = 4% to 13%).
GRADE Moderate certainty.
We recommend that trialists use self-sampling kits to increase retention in trails for which this is possible.
See Resource bundle below for details on how to use self-sampling kits.
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 self-sampling kits. The chart below shows the impact of an absolute increase of 9% (95% CI = 4% to 13%). Retention is now 78%, which means our best estimate is that you would now be only 2 responses short.