The 'equal weight view' of peer disagreement appears to have a sort of rising popularity. At least, one sees it assumed quite often. This view is something along these lines:
If I and another person (let's call her Sally) are epistemic peers,
I should always give Sally's evaluation of the evidence equal weight to my own
(to the extent that we are epistemic peers).
I think this is pretty clearly false. As I've said before, it gets an apparent plausibility from thinking of cases of third parties evaluating in the dark -- i.e., if someone does not know anything (or anything significant) about the evaluations ore evidence beyond the fact that Sally and I are epistemic peers, they should give us equal weight in their evaluations, all other things being equal. But I myself have not just the fact that Sally and I are epistemic peers; I also have the evidence, my evaluation of it, and any checking I have done to make sure I have collected, organized, and evaluated the evidence properly. This is not irrelevant to my assessment. And so, as I have said before, I think it's clear that the disagreement of my epistemic peer serves as nothing more than a checking mechanism. The fact that my epistemic peer disagrees with me is significant, just as (when I am doing a calculation) my failure to come to exactly the same result as before is significant. But this is just a matter of checking, and is no different from any other form of checking, and so makes the epistemic peer just one checking mechanism out of any others I might be using. If I count out a wad of dollar bills, and then count it out again, and then count it out again, and get $50 twice and $49 once, the fact that I was equally competent and working with the same evidence in all three cases is not relevant to anything. Likewise, if I count it once and get $50, Sally counts it and gets $49, and then I check my work to get $50.
I think the proper view to take is what Adam Elga calls the 'proper reasons view', or at least some variation of it. On various forms of the proper reasons view, the fact of disagreement does not matter; what matters is which of you has actually evaluated the evidence correctly. Elga has an argument against such views (PDF), one that we can call the 'bootstrapping objection'. Suppose it were legitimate to give your views greater weight than those of your epistemic peers. Then it would follow that it's legitimate to bootstrap. You could make yourself an epistemic superior simply by noting cases of disagreement and taking it to be the case that the friend made most of the errors. This would obviously be absurd, so (the argument goes) the proper reasons view is absurd.
But the proper reasons view, as far as I can see, doesn't actually have this result. The result of the proper reasons view is not that I and Sally are not peers, but that (as it happened) Sally erred in a way that people of our epistemic abilities can err, and (as it happened) I did not. This sheds no light on whether I am a better evaluator than Sally. I could only legitimately account myself a superior if I had good reasons to think that, in fact, Sally was not as good as I was at evaluating this sort of evidence. (And even that, it should be said, means very little. Even if Sally is not as good as I am, or indeed even if her abilities are considerably less than mine, she still may be good enough to be a good checker of my results. So even if Sally and I are not epistemic peers, we can still have the same relationship we do if we are.) But the mere fact that Sally made a mistake -- or, in fact, many mistakes -- is irrelevant to this, if they are the sort of mistakes that can be made under normal conditions by people of such-and-such epistemic competence and ability. And ex hypothesi they have to be -- given that Sally and I are epistemic peers, Sally's mistakes are exactly the same sort of mistakes I could make. Even if Sally makes many such mistakes, it tells me nothing about her competence, or whether she is my equal; even a run of mistakes is nothing more than bad luck -- bad luck that I could just as easily have had, even though in fact I'm sure I didn't. Even persistent mistakes on the part of Sally are not relevant if the mistakes are of the sort possible to people of the same ability as myself. And indeed, it would make nonsense of the notion of 'epistemic peer' to say otherwise; how could I reasonably take the mistakes as evidence of inferiority if they're of the sort that are consistent with equality?
It's often overlooked that if two people are epistemic peers it follows that they can, in principle, make the same sort of mistakes; so the mere fact that one of them makes a mistake sheds no light on whether they are really peers or not, as long as the mistake is of the right sort. The very fact that they are epistemic peers implies that they have the same region of possible-mistakes-compatible-with-their-ability. So it is entirely consistent with their being epistemic peers that one should make a mistake falling within that region and the other not. The proper reasons view does not change this; and therefore you can't, in fact, bootstrap yourself to superiority by noting mistakes. They would have to be mistakes of the right sort -- and mistakes of the right sort would be genuine evidence that the classification of the other person as an epistemic peer is incorrect. (Again, this classification is not, in fact, a particularly important issue, given the role epistemic peers actually are able to have in inquiry.)
