### Mental Model

Base Rates, Base Rate Fallacy, and Bayes Theorem

### Summary

A Base Rate is a type of probability that describes the likelihood of an event when no new or more specific information is available.

Another way to think about it is that Base Rates cover the general or usual chance that something will (or will not) happen, as opposed to recent or more specific information that may alter the probability for the event.

The key idea is that Base Rates cover what usually happens if nothing new or interesting occurs to impact the outcome.β

Base Rate Neglect or Base Rate Fallacy refers to our tendency to ignore data about what usually happens and instead focus just on new, recent, or interesting information.

Bayes Theorem is a mathematical equation where you can input the Base Rate for an event along with the probabilities associated with new information to get the actual overall probability for the event.β