 In contrast, a discordant pair is a pair of two-variable observations such that

That is, if one pair contains a higher value of "X" then the other pair contains a higher value of "Y".The Kendall tau distance between two series is the total number of discordant pairs.The Kendall tau rank correlation coefficient, which measures how closely related two series of numbers are, is proportional to the difference between the number of concordant pairs and the number of discordant pairs.