Use of the tetrachoric correlation model in assessing clinical tests

Categorical data on n patients are classified according to the results on an initial clinical test T, and also with respect to a subsequent and definitive diagnosis D. In this paper the sensitivity (=), specificity (=) and predictive values (=_v) are discussed with reference to the tetrachoric correlation model based on the bivariate normal density (e.g. PEARSON, 1901; KENDALL and STUART, 1972, II, p. 317). The result of HAMDAN (1970) concerning the equivalence of the tetrachoric r_t and the maximum likelihood estimate of the correlation coefficient is utilized in this paper to obtain a test of significance concerning r_t, and also the relation between the tetrachoric function w and the relative risk ψ for the 2X2 table.