I’m planning a few behavior intervention trials for the coming year (smoking cessation, alcohol reduction, etc.). I’m thinking of adopting a Bayesian group sequential design for these trials, as the analysis plans are fully Bayesian, and it doesn’t match well with thinking in terms of traditional power calculations and significance test.
One thing that I haven’t really seen a discussion about is the re-starting of a trial due to criteria that previously were met no longer being so. Here is an example:
- Let us assume that I have a success criteria P1 and a futility criteria P2.
- I have a follow-up interval of 3 months from randomization.
- I recruit for 6 months, and analyzing those who have responded to the 3 month follow-up at this time reveals that P2 is fulfilled. It seems that it is futile to continue recruitment, so I stop.
- However, there are still participants in the trial that are yet to report 3 month outcomes, and as they start reporting the P2 criteria is no longer fulfilled. Now it seems that it is not futile to continue, but P1 is not fulfilled.
My question is, should I then re-start recruitment after having stopped? What are your concerns with doing so versus not doing so?
From my perspective a Bayesian group sequential design should be the norm in behavior intervention trials, so guidance is very much welcome to help set a standard.