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The posterior probability is a type of conditional probability that results from updating the prior probability with information summarized by the likelihood via an application of Bayes' rule. [1]
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 ...
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 .
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 ().
where (|) denotes the posterior, (|) the likelihood, () the prior, and () the evidence (also referred to as the marginal likelihood or the prior predictive probability of the data). Note that the denominator p ( D ) {\displaystyle p(D)} is normalizing the total probability of the posterior density p ( θ | D ) {\displaystyle p(\theta |D)} to ...
The prior probability may also quantify prior knowledge or information about . P ( B ∣ A ) {\displaystyle P(B\mid A)} is the likelihood function , which can be interpreted as the probability of the evidence B {\displaystyle B} given that A {\displaystyle A} is true.
Bayesian linear regression is a type of conditional modeling in which the mean of one variable is described by a linear combination of other variables, with the goal of obtaining the posterior probability of the regression coefficients (as well as other parameters describing the distribution of the regressand) and ultimately allowing the out-of-sample prediction of the regressand (often ...
Posterior = Likelihood × Prior ÷ ... this process can be interpreted as "support from independent evidence adds", and the log-likelihood is the "weight of evidence".