Kendall's tau

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.