On the Representation of Ignorance
C. Villegas · Journal of the American Statistical Association · 1977
An invariance principle is used to show that λ−1 is the prior density representing ignorance concerning the parameter λ of a Poisson process, and a compatibility principle is applied to find an ignorance prior for the probabilities pi of the categories in a multinomial model. It is shown that IIpi −1 is the only positive and exchangeable prior that satisfies the compatibility condition.