The Kuder-Richardson formula (21) as a split-half coefficient,and some remarks on its basic assumption

Case IV of the Kuder-Richardson series, their formula (21), is derived as a generalized split-half Spearman-Brown coefficient. The basic assumption employed is shown to be sufficient to justify the various assumptions used in derivations by other authors. Some of the implications of this assumption are discussed.     

The average spearman rank correlation coefficient

A method is derived for finding the average Spearman rank correlation coefficient ofN sets of ranks with a single dependent or criterion ranking ofn items without computing any of the individual coefficients. Procedures for calculating the exact distribution of _av for small values ofN andn are described for the null case. The first four moments about zero of this distribution are derived, and it is concluded that for samples as small asN=4 andn=4 the normal distribution can be used safely in testing the hypothesis _av=0.This problem first came to the writer's attention in discussions with Dr. Dean J. Clyde.     

A note on correcting for chance success in objective tests

The conventional scoring formula to correct for guessing is derived and is compared with a regression method for scoring which has been recently proposed by Hamilton. It is shown that the usual formula,S=R–W/(n–1), yields a close approximation (correct within one point) to the maximum-likelihood estimate of an individual's true score on the test, if we assume that the individual knows or does not know the answer to each item, that guessing at unknown items is random, and that success at guessing is governed by the binomial law. It is also shown that the usual scoring formula yields an unbiased estimate of the individual's true score, when the true score is defined as the mean score over an indefinitely large number of independent attempts at the test or at equivalent (parallel) tests.