The mathematical theory of communication was applied to psychological testing and a formula for the entropy of a test was derived assuming an information transmission from the source of the postulated true score distribution to the destination, i.e. the observer. Two test score models, i.e. a simplified model of bivariate normal distribution of true and observed scores and the binomial error model, were both employed to calculate the entropy of the actual test data. The amount of information transmitted per subject was found to be surprisingly low. Under these test models, the rate of information transmission varied monotonically with test reliability. However, some of the results promised the possibility that a more detailed analysis of relationship between test structure and its entropy might clarify the meaning of the new measure.
