Test skewness and kurtosis as functions of item parameters

Indexes of skewness and kurtosis for a test-score distribution are expressed in terms of item parameters. Both are shown to depend, in part, on item means, variances, and covariances. The index of skewness depends also on trivariances. A trivariance is a product moment involving first powers of deviation scores for three items. The index of kurtosis depends on quadrivariances, as well as trivariances. A quadrivariance is a product moment involving first powers of deviation scores for four items. Empirical data are presented for responses of groups of subjects to 25 triads and 25 tetrads of items from five tests.Certain parts of this article represent the results of doctoral research conducted by Hundleby and Goldstein under the direction of Ray in the Department of Psychology at Pennsylvania State University. The authors are indebted to Professor Lester Guest and Professor William Lepley for their supervisory assistance in the final stages of the two dissertations during the absence of the senior author.