Bayesian statistics

a branch of statistics that involves learning from evidence as it accumulates. It is based on Bayes’ Rule (or Bayes’ Theorem), a mathematical equation that expresses how the prior (initial) probability of an event (or the probability that a hypothesis is true or the distribution for an unknown quantity) changes to a posterior (updated) probability given relevant new evidence. For example, in the diagnosis of a condition in an individual patient, a prior probability of a diagnosis may be based on the known prevalence of that condition in a relevant population. This can be updated to a posterior probability based on whether the result of a diagnostic test for that condition in that patient is positive or negative.

Reference

Goodman CS. HTA 101: Introduction to Health Technology Assessment. Bethesda,MD: National Library of Medicine (US); 2014.