The A/B Test for Decision Making

Confirmation bias – i.e. overweighting evidence that supports your view and underweighting evidence that doesn’t – is a well-established cognitive bias. Indeed, it often seems to be the case that when people are presented with evidence against their beliefs, they simply retrench further.

Several years ago, I came up with a trick that helps me avoid this.

The method is simple. In my mind, I make two columns, each of which represents one ‘hypothesis’.

For example, a few years ago my wife made the claim that I was a “bad driver”. I of course immediately became defensive and thought of all the evidence I could that supported my being a good driver: I had never been in an accident; had only received two speeding tickets since I started driving; etc.

Using this technique, I picture something like this in my mind:

For each piece of evidence, I then ask which hypothesis that evidence supports better and put it in that column. For example, let’s say we had the following pieces of evidence:

  • In my driving career:
    • I had gotten in one accident
    • I had gotten two speeding tickets
    • I often parked terribly
    • I had been in many near accidents
    • I seemed to drive much worse when other people were in the car
    • When asked, other people rated me as ‘below average’.

Using my method, in my mind I saw something like this:

Based upon this, I had to concede that the balance of the evidence suggested that, while I may not be a terrible driver, I certainly wasn’t as good a driver as I had thought.

I think the reason this framework works (at least for me) is that it forces me to start by treating the probability of each hypothesis being right as equal and then to consider all the evidence and how each piece supports the hypotheses.

I use this general construct all the time. Is a person being malicious or just lazy? Does God exist or not? Is a given policy likely to be helpful or hurtful?

Now if I were doing this more rigorously I suppose I would instead ask whether each peice of evidence refutes or falsifies each hypothesis. I’ll work on that. In the meantime, I’ve found this practice to be easy to do and effective in helping me think more clearly.

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