TY - JOUR T1 - Bayesian Inference: Statistical Gimmick or Added Value? JF - The Journal of Rheumatology JO - J Rheumatol SP - 794 LP - 796 DO - 10.3899/jrheum.110013 VL - 38 IS - 5 AU - SINDHU R. JOHNSON Y1 - 2011/05/01 UR - http://www.jrheum.org/content/38/5/794.abstract N2 - Use of the Bayesian inferential paradigm, although uncommon, is increasing in the rheumatology literature. The Bayesian school of statistical inference is based on the work of Reverend Thomas Bayes1. Using Bayes’s theorem, observations are used to calculate the probability that a hypothesis is true. Pre-existing data or knowledge are expressed as a prior probability distribution or “prior.” New observations are made and expressed as a likelihood. Using the new data, the degree of confidence in the hypothesis is recalculated. This process thus informs the reader on how this new information should change the way we think2. This contrasts with the “frequentist” statistical paradigm. Using frequentist inference, a null hypothesis of “no effect” and an alternative hypothesis that a “treatment effect exists” are specified before the conduct of a study. An allowable false-positive rate (i.e., level of significance, p value) is often arbitrarily set at 5%. A treatment is said to be effective if the p value is < 0.05 or the 95% confidence interval excludes a null effect. Bayesian statistics was the dominant statistical paradigm — prior to introduction of the now mainstream frequentist statistics. Its wide-scale application was limited by its computational complexity. In recent decades, its application became feasible with the introduction of faster computers and user-friendly statistical software. The more common day-to-day usage of the Bayesian inferential paradigm can be seen in meteorology (e.g., 20% probability of rain tomorrow) or the computer sciences (90% probability that this e-mail is spam and thus should go to the junk mail folder). In clinical medicine, we regularly apply Bayes’s theorem when interpreting a diagnostic test. The post-test probability of disease (e.g., inflammatory back disease) is determined by our pre-test probability … Address correspondence to Dr. S. Johnson, Division of Rheumatology, Ground Floor, East Wing, Toronto Western Hospital, 399 Bathurst Street, Toronto, Ontario, Canada, M5T 2S8. E-mail: Sindhu.Johnson{at}uhn.on.ca ER -