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In statistics, the score, score function, efficient score〔Cox & Hinkley (1974), p 107〕 or informant indicates how sensitively a likelihood function depends on its parameter . Explicitly, the score for is the gradient of the log-likelihood with respect to . The score plays an important role in several aspects of inference. For example: : *in formulating a test statistic for a locally most powerful test;〔Cox & Hinkley (1974), p 113〕 : *in approximating the error in a maximum likelihood estimate;〔Cox & Hinkley (1974), p 295〕 : *in demonstrating the asymptotic sufficiency of a maximum likelihood estimate;〔 : *in the formulation of confidence intervals;〔Cox & Hinkley (1974), p 222–3〕 : *in demonstrations of the Cramér–Rao inequality.〔Cox & Hinkley (1974), p 254〕 The score function also plays an important role in computational statistics, as it can play a part in the computation of maximum likelihood estimates. ==Definition== The score or efficient score 〔 is the gradient (the vector of partial derivatives), with respect to some parameter , of the logarithm (commonly the natural logarithm) of the likelihood function (the log-likelihood). If the observation is and its likelihood is , then the score can be found through the chain rule: : Thus the score indicates the sensitivity of (its derivative normalized by its value). Note that is a function of and the observation , so that, in general, it is not a statistic. However in certain applications, such as the score test, the score is evaluated at a specific value of (such as a null-hypothesis value, or at the maximum likelihood estimate of ), in which case the result is a statistic. In older literature, the term "linear score" may be used to refer to the score with respect to infinitesimal translation of a given density. This convention arises from a time when the primary parameter of interest was the mean or median of a distribution. In this case, the likelihood of an observation is given by a density of the form . The "linear score" is then defined as : 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Score (statistics)」の詳細全文を読む スポンサード リンク
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