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In Bayesian statistics, the posterior probability is the probability of the parameters given the evidence , and is denoted (|). It contrasts with the likelihood function , which is the probability of the evidence given the parameters: p ( X | θ ) {\displaystyle p(X|\theta )} .
An informative prior expresses specific, definite information about a variable. An example is a prior distribution for the temperature at noon tomorrow. A reasonable approach is to make the prior a normal distribution with expected value equal to today's noontime temperature, with variance equal to the day-to-day variance of atmospheric temperature, or a distribution of the temperature for ...
Update the point with least likelihood with some Markov chain Monte Carlo steps according to the prior, accepting only steps that keep the likelihood above . end return Z {\displaystyle Z} ; At each iteration, X i {\displaystyle X_{i}} is an estimate of the amount of prior mass covered by the hypervolume in parameter space of all points with ...
The posterior probability of a model depends on the evidence, or marginal likelihood, which reflects the probability that the data is generated by the model, and on the prior belief of the model. When two competing models are a priori considered to be equiprobable, the ratio of their posterior probabilities corresponds to the Bayes factor .
The posterior distribution should have a non-negligible probability for parameter values in a region around the true value of in the system if the data are sufficiently informative. In this example, the posterior probability mass is evenly split between the values 0.08 and 0.43.
Bayesian statistics; Posterior = Likelihood × Prior ÷ Evidence: Background; Bayesian inference; Bayesian probability; Bayes' theorem; Bernstein–von Mises theorem; Coherence; Cox's theorem; Cromwell's rule; Likelihood principle; Principle of indifference; Principle of maximum entropy; Model building; Conjugate prior; Linear regression ...
In Bayesian probability theory, if, given a likelihood function (), the posterior distribution is in the same probability distribution family as the prior probability distribution (), the prior and posterior are then called conjugate distributions with respect to that likelihood function and the prior is called a conjugate prior for the likelihood function ().
Given a vector of parameters to determine, a prior probability () over those parameters and a likelihood (,) for making observation , given parameter values and an experiment design , the posterior probability can be calculated using Bayes' theorem