- Kendall tau rank correlation coefficient
The

**Kendall tau rank correlation coefficient**(or simply the**Kendall tau coefficient**,**Kendall's τ**or**tau test(s)**) is anon-parametric statistic used to measure thedegree of correspondence between tworanking s and assessing thesignificance of this correspondence. In other words, it measures the strength of association of thecross tabulations .It was developed by

Maurice Kendall in 1938.**Definition**The Kendall tau coefficient (τ) has the following properties:

* If the agreement between the two rankings is perfect (i.e., the two rankings are the same) the coefficient has value 1.

* If the disagreement between the two rankings is perfect (i.e., one ranking is the reverse of the other) the coefficient has value −1.

* For all other arrangements the value lies between −1 and 1, and increasing values imply increasing agreement between the rankings. If the rankings are completely independent, the coefficient has value 0 on average.Kendall tau coefficient is defined

: $au\; =\; frac\{n\_c-n\_d\}\{frac\{1\}\{2\}\{n(n-1)$

where "$n\_c$" is the number of

concordant pairs , and "$n\_d$" is the number ofdiscordant pairs in the data set.The

denominator in the definition of $au$ can be interpreted as the total number of pairs of items. So, a high value in thenumerator means that most pairs are concordant, indicating that the two rankings are consistent. Note that a tied pair is not regarded as concordant or discordant. If there is a large number of ties, the total number of pairs (in the denominator of the expression of $au$) should be adjusted accordingly.**Tau a, b and c***"Tau a" — This tests the strength of association of the cross tabulations when both variables are measured at the

ordinal level but makes no adjustment for ties.

*"Tau b" — This tests the strength of association of the cross tabulations when both variables are measured at the ordinal level. It makes adjustments for ties and is most suitable for squaretable s. Values range from −1 (100% negative association, or perfect inversion) to +1 (100% positive association, or perfect agreement). A value of zero indicates the absence of association.

*"Tau c" — This tests the strength of association of the cross tabulations when both variables are measured at the ordinal level. It makes adjustments for ties and is most suitable forrectangular tables. Values range from −1 (100% negative association, or perfect inversion) to +1 (100% positive association, or perfect agreement). A value of zero indicates the absence of association.**See also***

Correlation

*Kendall tau distance

*Kendall's W

*Spearman's rank correlation coefficient **References***cite paper | author = Abdi, H. | title = [

*http://www.utdallas.edu/~herve/Abdi-KendallCorrelation2007-pretty.pdf*] (2007) Kendall rank correlation. In N.J. Salkind (Ed.): Encyclopedia of Measurement and Statistics. Thousand Oaks (CA): Sage.| year = 2007 |

* Kruskal, W.H. (1958) "Ordinal Measures of Association", Journal of the American Statistical Association, 53(284), 814-861.

* Kendall, M. (1948) "Rank Correlation Methods", Charles Griffin & Company Limited

* Kendall, M. (1938) "A New Measure of Rank Correlation", Biometrika, 30, 81-89.**External links*** [

*http://rsscse.org.uk/ts/bts/noether/text.html Why Kendall tau?*]

* [*http://www.wessa.net/rwasp_kendall.wasp Online software: computes Kendall's tau rank correlation*]

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**Kendall rank correlation coefficient (tau)**— Ken·dall rank correlation coefficient (tau) (kenґdəl) [Maurice George Kendall, British statistician, 1907â€“1983] see under coefficient … Medical dictionary**Kendall rank correlation coefficient**— a rank correlation coefficient used when both variables represent ordinal data in a limited number of grades, such as the categories none, mild, moderate, and severe, so that multiple samples can be assigned to each grade; called also Kendall tau … Medical dictionary**Spearman's rank correlation coefficient**— In statistics, Spearman s rank correlation coefficient or Spearman s rho, named after Charles Spearman and often denoted by the Greek letter ho (rho) or as r s, is a non parametric measure of correlation ndash; that is, it assesses how well an… … Wikipedia**Correlation coefficient**— may refer to: Pearson product moment correlation coefficient, also known as r, R, or Pearson s r, a measure of the strength of the linear relationship between two variables that is defined in terms of the (sample) covariance of the variables… … Wikipedia**Rank correlation**— In statistics, rank correlation is the study of relationships between different rankings on the same set of items. It measures the correspondence between two rankings and assesses its significance. Correlation coefficientsTwo of the more popular… … Wikipedia**Kendall tau**— Kendall rank correlation coefficient … Medical dictionary**Kendall tau distance**— The Kendall tau distance is a metric that counts the number of pairwise disagreements between two lists. The larger the distance, the more dissimilar the two lists are. Kendall tau distance is also called bubble sort distance since it is… … Wikipedia**Kendall rank correlation**— noun a nonparametric measure of the agreement between two rankings • Syn: ↑tau coefficient of correlation, ↑Kendall s tau • Topics: ↑statistics • Hypernyms: ↑Kendall test … Useful english dictionary**Kendall**— may refer to:Places;United Kingdom *Kendal, a town in the Lake District of England, after which several other places are named;Australia *Kendall, New South Wales, Australia;Canada *Kendal, Saskatchewan;Indonesia *Kendal Regency, a regency in… … Wikipedia**Tau (disambiguation)**— Tau is the 19th letter of the Greek alphabet.Tau may also refer to:In geography: * Tau, Norway, a small town in western Norway * Tău, two villages in Romania * Tau, Samoa (Taokinaū), an island in the Manuokinaa Island Group of American Samoa *… … Wikipedia