Kuder-Richardson coefficient

n. This is Kuder-Richardson formula 20, which is a widely used measure of internal consistency of tests in which only two responses are possible (correct-incorrect or true-false, for example). KR20 is equal to the average of all possible split-half correlations corrected for attenuation.

\(KR20=(\frac{n}{n-1})\times(\frac{Variance-\sum{pq}}{Variance})\)

where \(Variance\) = variance of total scores on the test.