Test scores examined with the lexis ratio

The Lexis Ratio is discussed in its application to distributions of test scores where the items of the test can be assumed to be of equal difficulty. The ratio indicates the extent to which inter-individual variation operates as a source of the variance. The concept is related to the Lexis, Bernoulli, and Poisson distributions and illustrated by urn schemata. The Ratio is applied to the scores of 560 university freshmen on theRobinson Reading Test. The relation of the Lexis Ratio to the Kuder-Richardson estimation of reliability is also discussed and the latter authors' case IV is rewritten explicitly in terms of the Ratio.