Amalgamating evidence of different kinds for the same hypothesis into an overall confirmation is analogous, I argue, to amalgamating individuals’ preferences into a group preference. The latter faces well-known impossibility theorems, most famously “Arrow’s Theorem”. Once the analogy between amalgamating evidence and amalgamating preferences is tight, it is obvious that amalgamating evidence might face a theorem similar to Arrow’s. I prove that this is so, and end by discussing the plausibility of the axioms required for the theorem.

An electoral evaluation of a set of expert opinions proceeds by treating the experts as voters. Although this method allows us to formalise our naive views about how to take expert advice, the formalisations are plagued by paradoxes which parallel those found in literature on social aggregation devices. This parallel suggests that our naive views about taking expert advice are in as much need of revision as our naive views about deriving group preferences from individual preferences. * I am indebted (...) to Joseph Hanna for a number of criticisms and corrections to a previous draft. (shrink)