9eB1 comments on What Bayesianism taught me - Less Wrong

62 Post author: Tyrrell_McAllister 12 August 2013 06:59AM

You are viewing a comment permalink. View the original post to see all comments and the full post content.

Comments (201)

You are viewing a single comment's thread. Show more comments above.

Comment author: Anatoly_Vorobey 11 August 2013 06:52:14AM 13 points [-]

A typical situation is that there's a contentious issue, and some anecdotes reach your attention that support one of the competing hypotheses.

You have three ways to respond:

  1. You can under-update your belief in the hypothesis, ignoring the anecdotes completely
  2. You can update by precisely the measure warranted by the existence of these anecdotes and the fact that they reached you.
  3. You can over-update by adding too much credence to the hypothesis.

In almost every situation you're likely to encounter, the real danger is 3. Well-known biases are at work pulling you towards 3. These biases are often known to work even when you're aware of them and trying to counteract them. Moreover, the harm from reaching 3 is typically far greater than the harm from reaching 1. This is because the correct added amount of credence in 2 is very tiny, particularly because you're already likely to know that the competing hypotheses for this issue are all likely to have anecdotes going for them. In real-life situations, you don't usually hear anecdotes supporting an incredibly unlikely-seeming hypothesis which you'd otherwise be inclined to think as capable of nurturing no anecdotes at all. So forgoing that tiny amount of credence is not nearly as bad as choosing 3 and updating, typically, by a large amount.

The saying "The plural of anecdotes is not data" exists to steer you away from 3. It works to counteract the very strong biases pulling you towards 3. Its danger, you are saying, is that it pulls you towards 1 rather than the correct 2. That may be pedantically correct, but is a very poor reason to criticize the saying. Even with its help, you're almost always very likely to over-update - all it's doing is lessening the blow.

Perhaps this as an example of "things Bayesianism has taught you" that are harming your epistemic rationality?

A similar thing I noticed is disdain towards "correlation does not imply causation" from enlightened Bayesians. It is counter-productive.

Comment author: 9eB1 12 August 2013 04:28:29AM *  5 points [-]

A typical situation is that there's a contentious issue, and some anecdotes reach your attention that support one of the competing hypotheses.

It is interesting that you think of this as typical, or at least typical enough to be exclusionary of non-contentious issues. I avoid discussions about politics and possibly other contentious issues, and when I think of people providing anecdotes I usually think of them in support of neutral issues, like the efficacy of understudied nutritional supplements. If someone tells you, "I ate dinner at Joe's Crab Shack and I had intense gastrointestinal distress," I wouldn't think it's necessarily justified to ignore it on the basis that it's anecdotal. If you have 3 more friends who all report the same thing to you, you should rightly become very suspicious of the sanitation at Joe's Crab Shack. I think the fact that you are talking about contentious issues specifically is an important and interesting point of clarification.