Conditional Probability

Questions

What is Conditional Probability?

Conditional probability is the likelihood of an event given that another event has already occurred. New information changes the odds, sometimes dramatically, as the famous Monty Hall puzzle shows.

How do you use Conditional Probability?

To use it, ask what a statistic means for someone in your situation, update your plans when conditions change, and consider people's circumstances before judging their behaviour.

When does Conditional Probability matter?

Conditional Probability is one of the 68 mental models for evidence, the situations where you ask: Is this really true? Within that, it belongs to “Reading the numbers”, alongside Base Rate Fallacy, Bayes’ Theorem and Central Limit Theorem.

What is an example of Conditional Probability?

Two stories show it at work: The Monty Hall problem (1990) and FICO (1989). Both are told in full in The Mental Models Daily Almanac, which has two stories for each of its 365 models.

Which mental models are related to Conditional Probability?

Bayes’ Theorem, Conjunction Fallacy and Fundamental Attribution Error. Conditional Probability itself comes from statistics and probability.