Thinking method · Tetlock & Gardner, Superforecasting

Updating by degrees

Moving a belief a proportionate amount when new evidence arrives, instead of all or nothing.

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Moving a belief a proportionate amount when new evidence arrives, instead of all or nothing.

The steps

1. State your current belief as a rough percentage. Any number beats "I think so".
2. When evidence arrives, ask: how much more likely is this evidence if I am right than if I am wrong?
3. Move your number in that direction — usually by less than instinct suggests.
4. Write the new number and the reason beside it.
5. Look back periodically: were your 70%s right about seventy percent of the time?

When to use it

Any belief you will hold for a while and that evidence keeps arriving about.

What it will not do

Numbers do not make a guess into knowledge. They make it checkable, which is different and better.

Where it comes from: Tetlock & Gardner, Superforecasting. Described in our own words.