 A fully-fledged Bayesian approach to aggregation demands that the final credence be derived by Bayesian updating in light of the opinions held by each group member (Keeney and Raiffa 1993). Notice, this is also what a Bayesian individual should do to update on the credences of others. To do this properly, though, is very  complicated.[2]  It requires prior probabilities about what obtains in the world, as well as probabilities about how likely each group member is to develop their credences in light of what might obtain in world. This will not be practical in real cases.