Probability
A mathematical framework for describing uncertainty and likelihood.
Probability is a mathematical framework for describing uncertainty. A probability lies between zero and one in standard models, but its interpretation depends on the model: it may represent long-run frequency, or a degree of belief conditional on stated information and assumptions.
The probability of an event can change when relevant information is known. To reason about a test result or forecast, distinguish the chance of evidence given a condition from the chance of the condition given that evidence. Base rates matter; ignoring them can make a rare event seem much more likely than it is.
Probabilities are not guarantees about a single outcome. A model is only as useful as its assumptions, data, and fit to the question. When decisions depend on probability, consider the consequences of different errors, the time horizon, and whether new evidence should change the estimate.
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