A BAYESIAN TEST FOR A 2-WAY CONTINGENCY TABLE USING INDEPENDENCE PRIORS

One method of testing for independence in a two-way table is based on the Bayes factor, the ratio of the likelihoods under the independence hypothesis H and the alternative hypothesis HBAR. The main difficulty in this approach is the specification of prior distributions on the composite hypotheses H and HBAR. A new Bayesian test statistic is constructed by using a prior distribution on HBAR that is concentrated about the "independence surface" H. Approximations are proposed which simplify the computation of the test statistic. The values of the Bayes factor are compared with values of statistics proposed by Gunel and Dickey (1974), Good and Crook (1987), and Spiegelhalter and Smith (1982) for a number of two-way tables. This investigation suggests a strong relationship between the new statistic and the p-value.