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Bayesian estimator : ウィキペディア英語版 | Bayes estimator
In estimation theory and decision theory, a Bayes estimator or a Bayes action is an estimator or decision rule that minimizes the posterior expected value of a loss function (i.e., the posterior expected loss). Equivalently, it maximizes the posterior expectation of a utility function. An alternative way of formulating an estimator within Bayesian statistics is maximum a posteriori estimation. ==Definition== Suppose an unknown parameter θ is known to have a prior distribution . Let be an estimator of θ (based on some measurements ''x''), and let be a loss function, such as squared error. The Bayes risk of is defined as , where the expectation is taken over the probability distribution of : this defines the risk function as a function of . An estimator is said to be a ''Bayes estimator'' if it minimizes the Bayes risk among all estimators. Equivalently, the estimator which minimizes the posterior expected loss ''for each x'' also minimizes the Bayes risk and therefore is a Bayes estimator.〔Lehmann and Casella, Theorem 4.1.1〕 If the prior is improper then an estimator which minimizes the posterior expected loss ''for each x'' is called a generalized Bayes estimator.〔Lehmann and Casella, Definition 4.2.9〕
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