FDA Shows Interest in 18th Century Presbyterian Minister

Tuesday, January 31st, 2006

The Presbyterian minister at the heart of FDA Shows Interest in 18th Century Presbyterian Minister is Thomas Bayes, the creator of Bayesian statistics:

The frequentist approach, familiar to anyone who follows the news of clinical trials, measures the likelihood of an observed result having occurred by chance. That ‘just by accident’ possibility is the null hypothesis, and is usually realized in clinical studies by giving a placebo to some of the trial participants for comparison. Results are expressed as a ‘P value’, with (for example) a P of 0.01 meaning that if the trial were repeated over and over, only one per cent of those studies would show an equivalent result (or better) for the placebo as compared to the drug treatment.

Bayesian statistics, though, don’t address the likelihood that your observed results might have come out by random chance, but rather give you a likelihood of whether your initial hypothesis is true. (Ironically, that’s what many lay people think that’s what the standard approach does). That likelihood is compared to some initial hypothesis, which doesn’t have to be the just-by-accident null one. In fact, you can start with more than one hypothesis and compare things as you go along. One consequence of that setup is that Bayesian trial designs allow you to use the data that comes in to modify the trial while it’s still going on. That’s basically forbidden under the standard statistical approach, where the design and end points of the study have to be decided up front.

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