Prospective application of Bayesian monitoring and analysis in an "open" randomized clinical trial

We describe the prospective application of Bayesian monitoring and analysis in an ongoing large multi-centre, randomized trial in which interim results are released to investigators. Substantial variability in prior opinion led us to reject the use of elicited clinical priors for monitoring, in favour of archetypal prior distributions representing reasonable scepticism and enthusiasm. Likelihoods for odds ratios for different covariate values are derived from a logistic regression model, which allows us to incorporate information from prognostic factors without resorting to specialized software. Priors, likelihoods and posterior distributions are regularly reported to both an independent Data Monitoring Committee and the trial investigators.