This study investigated the unidimensional assumption underlying choice behavior by examining the transitivity properties of rats' choice behavior. In Experiment 1, two variables of reinforcement, amount and delay, were manipulated simultaneously in a two lever choice situation. The conditions of strong transitivity were not present in either reponse count or indifference-measured choice behavior, indicating that choice behavior was not distributed along a single dimension with ratio scale characteristics. Moderate transitivity conditions were characteristic of both response and indifference- measured choice which was consistent with a single dimension possessing interval scale characteristics. In Experiment 2, only one reinforcement variable, amount, was manipulated. Strong transitivity was present in both response and indifference measures of choice, indicating that subjects' choice behavior was consistent with a single dimension with ratio scale characteristics. In addition, one of two subjects in Experiment 1 and two of two subjects in Experiment 2 fit Baum's expression of the matching law with response-count measured choice. The indifference measure of choice failed to fit the matching law in either experiment. The measure of choice which fit the matching law also conformed to a single dimension with interval scale characteristics. Since the response-count measure of choice behavior in both Experiments 1 and 2 was moderately transitive, the transitivity properties were consistent with fits to the matching law. The occasional presence of such behaviors as biting the levers, chewing on the cue lights and position bias may have decreased subjects' sensitivity to the amount of reinforcement variable and contributed to undermatching. The indifference measure of choice exhibited moderate transitivity in both experiments but did not fit the matching law. These results show that tests of transitivity are useful in examining the characteristics of the functional relation between behavior and its reinforcing consequences. Further research is required to determine the usefulness and the limitations of the indifference measure of choice behavior. The results were similar to other investigators' in showing that strong transitivity was not an automatic property of choice behavior and must be tested rather than assumed.

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