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The ratio estimator is a statistical parameter and is defined to be the ratio of means of two variates. Ratio estimates are biased and corrections must be made when they are used in experimental or survey work. The ratio estimates are asymmetrical and symmetrical tests such as the t test should not be used to generate confidence intervals. The bias is of the order ''O''(1/''n'') (see big O notation) so as the sample size (''n'') increases, the bias will asymptotically approach 0. Therefore, the estimator is approximately unbiased for large sample sizes. ==Definition== Assume there are two characteristics – ''x'' and ''y'' – that can be observed for each sampled element in the data set. The ratio ''R'' is : The ratio estimate of a value of the ''y'' variate (''θ''''y'') is : where ''θ''''x'' is the corresponding value of the ''x'' variate. ''θ''''y'' is known to be asymptotically normally distributed.〔Scott AJ, Wu CFJ (1981) On the asymptotic distribution of ratio and regression estimators. JASA 76: 98–102〕 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「Ratio estimator」の詳細全文を読む スポンサード リンク
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