Bayesian inference featuring entropic priors

Abstract

The subject of this work is the parametric inference problem, i.e. how to infer from data on the parameters of the data likelihood of a random process whose parametric form is known a priori. The assumption that Bayes' theorem has to be used to add new data samples reduces the problem to the question of how to specify a prior before having seen any data. For this subproblem three theorems are stated. The first one is that Jaynes' Maximum Entropy Principle requires at least a constraint on the expected data likelihood entropy, which gives entropic priors without the need of further axioms. Second I show that maximizing Shannon entropy under an expected data likelihood entropy constraint is equivalent to maximizing relative entropy and therefore reparametrization invariant for continuous-valued data likelihoods. Third, I propose that in the state of absolute ignorance of the data likelihood entropy, one should choose the hyperparameter α of an entropic prior such that the change of expected data likelihood entropy is maximized. Among other beautiful properties, this principle is equivalent to the maximization of the mean-squared entropy error and invariant against any reparametrizations of the data likelihood. Altogether we get a Bayesian inference procedure that incorporates special prior knowledge if available but has also a sound solution if not, and leaves no hyperparameters unspecified. © 2007 American Institute of Physics.