juniorProbability
What is conditional probability?
Updated May 17, 2026
Short answer
Conditional probability is the probability of an event given that another event has occurred.
Deep explanation
Defined as P(A|B) = P(A ∩ B) / P(B), conditional probability updates beliefs based on known information. It is fundamental in Bayesian reasoning and decision-making under uncertainty.
Real-world example
Probability of having a disease given a positive medical test.
Common mistakes
- Confusing P(A|B) with P(B|A).
Follow-up questions
- What is Bayes’ theorem?
- Why is normalization needed?