====== 肯德尔和谐系数 (Kendall's Coefficient of Concordance) ======

  * 它是被用来表示多列等级变量相关程度的指标。
    *  It was used as an indicator of the degree of correlation of multicolumn ranking variables.
  * 常用于K个评定者对N个事物进行等级评定，考察这K个评定者之间评分的一致性。
    * It is commonly used to rate N things by K raters and examine the consistency of ratings among these K raters.

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  * 其中 Ri 是每一个被评价事物的 K 个等级之和，K 为评定者的个数，N 为被评价的事物的个数。
    * where Ri is the sum of K ratings for each thing evaluated, K is the number of raters, and N is the number of things evaluated.
  * W可以看作是所有可能的评定者对评定等级的 Spearman 相关系数的函数：{{:第十二章:12.7:rsis.svg}}
    * W can be viewed as a function of the Spearman correlation coefficients of all possible raters for the rating scale.