The Advantages of a Run-in Period

The use of a run-in period is particularly valuable in longer-term trials. This is where you really need the participant to be adherent over months or years. And every patient who drops out after they've randomised or stops taking the intervention after randomisation, you will lose power. So the reason that you do a run-on period is to try and make sure that you only recruit into the trial the people who are most likely to remain adherent in the longer term.