How do you evaluate ‘expert’ opinion?

None of us are in a position to figure out everything for ourselves. We are all dependent on experts in specific fields for knowledge. While an expert’s reputation and record of reliability and honesty can and should be factored in, we don’t want to unquestioningly accept the assertions of authorities since it is possible that they may be mistaken or not as expert or knowledgeable as they claim to be or may even be lying

So to what extent is it reasonable to depend on experts? Bertrand Russell in his 1941 book Let the People Think suggested that rather than depend on this or that expert, one should look at the views of the aggregate of experts and draw the following reasonable inferences:

  1. “that when the experts are agreed, the opposite opinion cannot be held to be certain;
  2. that when they are not agreed, no opinion can be regarded as certain by a non-expert; and
  3. that when they all hold that no sufficient grounds for a positive opinion exist, the ordinary man would do well to suspend his judgment.”

That seems like a good rule of thumb.

But of course, you will rarely get unanimity among experts. There will almost always be dissenters. But at least when it comes to scientific matters, there often tends to be an overwhelming consensus and what I do is see what the dominant views are. So for example, in the case of global warming, since an overwhelming majority of climate scientists say that it is occurring and is man-made, Russell would say (according to rule (1)) that it would be foolish to insist that they are wrong. Similarly, since an overwhelming majority of biologists accept the theory of evolution as the means by which speciation occurred, Russell would say that it would be silly to confidently deny it. At most one should voice tentative dissent.

When it comes to economic or political questions where there is often not only no unanimity but not even a dominant consensus, rule (2) comes into play and it is wise to not place one’s faith too strongly on one particular view.


  1. Robert Allen says

    I modulate those rules with the extra criterion of known bias. For example, a relatively large percentage of Biblical scholars are Christians, but it would be fair to suspect a strong bias influencing their conclusions that skews the percentage. In an extreme case, some Christian “experts” have a statement of faith in which they promise never to change their position no matter what evidence they find. I think a jury would be right to completely ignore “expert” testimony from such a person.

  2. Scott says

    Robert, I see an inherent contradiction in Biblical scholars being Christian, in that they can’t be objective, so any statements they make would be suspect. Yet another reason to toss the whole thing out.

    Mano, one thing I’ve noticed is that conservatives tend to be less trusting of experts than liberals. Have you noticed this tendency?

  3. says


    Yes, I have noticed it. I think it arises because expert and informed analysis usually results in conclusions that are anathema to conservatives and so they find it easier to dismiss experts altogether.

    As someone (I think Stephen Colbert) said, “Reality has a well-known liberal bias.”

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