Bayes' Theorem let's us find out the probability of a cause given its effect. $ P(A|B) = \frac{P(B|A)P(A)}{P(B)} $ For example, we know that as you age, more health problems occur. Then we can also know that if you are 50 and feel abdominal pain, the probability of it being cancer is higher than if you're 20. ## Updating with New Evidence Baye's Theorem is at core of Bayesian Statistics, an approach that assigns probabilities to [[Hypothesis|hypotheses]], rather than data.