Applying Bayes and Beginning Classiers. Greg Kochanski http://kochanski.org/gpk 25 January 2004 1 Odds Ratios Bayes Theorem can be particularly simple if there are only two models. In that
case, you can turn it into a nice rule for updating the Odds ratio of the two
models whenever you get new data. 1.1 What is an Odds Ratio? An odds ratio is just the ratio of the probabilities of two alternate outcomes.
Odds ratios are traditionally used for betting: one might say that The odds
against Distant Thunder are nine to one to mean that the horse is nine times
more likely to lose than to win. In general, for event X under conditions C, the
odds ratio is R(X|C) = P (X|C) P (