A note on the estimation of test reliability by the Kuder-Richardson formula (20)

The Kuder-Richardson formula (20) is rewritten to be identical with the simplest formula, (21), except for the addition of a term involving the standard deviation, _p , of the itemp's. If _p can be estimated, a rapid and superior estimate of test reliability is possible in contrast to the simpler formula (21) used when the number of items and mean and standard deviation of test scores are known.Kuder, G. F. and Richardson, M. W. The theory of the estimation of test reliability.Psychometrika. 1937, 2, 151–160.