No. 234 · Evidence · Equations
Frequentists vs Bayesians
Probability can mean how often something happens, or how strongly you believe it will.
In the Almanac
“The lost Scorpion”, 1968 · “Metron”, 2011
Both stories in full, three ways to use it and where it misleads.
Get the AlmanacQuestions
What is Frequentists vs Bayesians?
Frequentists define probability as long-run frequency across repeated trials. Bayesians define it as a degree of belief that starts with a prior and updates as evidence arrives. Both are useful, in different situations.
How do you use Frequentists vs Bayesians?
Use frequency thinking when you can gather lots of repeat data, like commute times. Use Bayesian thinking for one-off, high-stakes choices: state your starting belief, then let every result, including every failure, move it.
When does Frequentists vs Bayesians matter?
Frequentists vs Bayesians 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 Frequentists vs Bayesians?
Two stories show it at work: The lost Scorpion (1968) and Metron (2011). 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 Frequentists vs Bayesians?
Bayes’ Theorem, Monte Carlo Simulation and Foxes vs Hedgehogs. Frequentists vs Bayesians itself comes from equations.