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In statistics, McKay's approximation of the coefficient of variation is a statistic based on a sample from a normally distributed population. It was introduced in 1932 by A. T. McKay. Statistical methods for the coefficient of variation often utilizes McKay's approximation.〔.〕 Let , be independent observations from a normal distribution. The population coefficient of variation is . Let and denote the sample mean and the sample standard deviation, respectively. Then is the sample coefficient of variation. McKay’s approximation is : Note that in this expression, the first factor includes the population coefficient of variation, which is usually unknown. When is smaller than 1/3, then is approximately chi-square distributed with degrees of freedom. In the original article by McKay, the expression for looks slightly different, since McKay defined with denominator instead of . McKay's approximation, , for the coefficient of variation is approximately chi-square distributed, but exactly noncentral beta distributed . == References== 〔 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「McKay's approximation for the coefficient of variation」の詳細全文を読む スポンサード リンク
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