When subjects are given open-ended stimulus situations allowing for responses at all possible stages of a developmental theory, the stage scores of individuals for each situation can be treated as scores on polychotomous items. Extensions of the concepts of difficulty and discriminating power from the dichotomous case to this ordinal category situation allow determination of these parameters. Assuming the trait being measured is distributed normally, stage difficulties or boundaries are deviates corresponding to cumulative proportions of subjects at each stage. Item discriminating powers are determined by the one factor loadings of the inter-item correlation matrix. Maximum-likelihood estimates of a subject's trait level can be determined from the parameters of each situation presented and that subject's answer pattern of stage scores. Data gathered in interviews to determine the level of moral development according to Lawrence Kohlberg's six-stage theory takes the above form. Results indicate that for different dilemmas, certain stages of reasoning are more easily attained than others, and when particular moral issues are analyzed across situations, an "entry" issue for various stages is indicated corresponding to Kohlberg's theory. (Author/MLP)