Some cognitive psychologists, who have tried to approach psychometric theories, say that the psychometric approach does not provide them with theories and methods with which they can deal with differential strategies. In this paper, a general latent trait model for differential strategies in cognitive processes is proposed which includes three different response levels: the nominal response level, the graded response level, and the dichotomous response level. The general graded response model is further classified into the homogeneous and the heterogeneous cases. Also the maximum likelihood estimation of the individual's latent trait is discussed. (Author/PN)