The FDA just gave us 25 pages on Bayesian inference in pivotal trials. The philosophical message is clear: Bayesian methods are welcome. Informative priors, borrowing from external data, direct interpretation of posterior probabilities—all explicitly endorsed. The operational message is different: pre-specify everything. Bayesian methods promise learning. Regulators demand commitment.
The most expensive decision in drug development (or product experimentation) is not starting a trial. It is continuing a zombie trial. Imagine you are at the interim analysis of a Phase II study. You have enrolled 50 of 100 patients. You have spent $10 million. The data is... underwhelming. The
Everyone says they want adaptive designs. Almost no one actually runs them. In decks, protocols, and FDA briefing books, “adaptive” has become a fashionable adjective—usually meaning a trial with one interim look, a conditional power calculation, and a long list of things you are not allowed to change. The
