tau (Kendall's)

n. A measure of association between two pairs of rankings such that no association = 0 and perfect association =1 using the formula

$ Tau=\frac{4p}{n(n-1)}-1 $

where \(n\) = the number of pairs and \(p\) = the sum of the rankings greater than a particular ranking to the right of the ranking, when one variable is ordered by the other variable.