Rao–Blackwell theorem
Statistical theorem / From Wikipedia, the free encyclopedia
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In statistics, the Rao–Blackwell theorem, sometimes referred to as the Rao–Blackwell–Kolmogorov theorem, is a result that characterizes the transformation of an arbitrarily crude estimator into an estimator that is optimal by the mean-squared-error criterion or any of a variety of similar criteria.
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The Rao–Blackwell theorem states that if g(X) is any kind of estimator of a parameter θ, then the conditional expectation of g(X) given T(X), where T is a sufficient statistic, is typically a better estimator of θ, and is never worse. Sometimes one can very easily construct a very crude estimator g(X), and then evaluate that conditional expected value to get an estimator that is in various senses optimal.
The theorem is named after C.R. Rao and David Blackwell. The process of transforming an estimator using the Rao–Blackwell theorem can be referred to as Rao–Blackwellization. The transformed estimator is called the Rao–Blackwell estimator.[1][2][3]