Let $X$ be a random vector distributed according to an exponential family with natural parameter $\theta \in \Theta$. We characterize conjugate prior measures on $\Theta$ through the property of linear posterior expectation of the mean parameter of $X : E\{E(X|\theta)|X = x\} = ax + b$. We also delineate which hyperparameters permit such conjugate priors to be proper.
@article{1176344611,
author = {Diaconis, Persi and Ylvisaker, Donald},
title = {Conjugate Priors for Exponential Families},
journal = {Ann. Statist.},
volume = {7},
number = {1},
year = {1979},
pages = { 269-281},
language = {en},
url = {http://dml.mathdoc.fr/item/1176344611}
}
Diaconis, Persi; Ylvisaker, Donald. Conjugate Priors for Exponential Families. Ann. Statist., Tome 7 (1979) no. 1, pp. 269-281. http://gdmltest.u-ga.fr/item/1176344611/