A STRUCTURAL MODEL OF THE HIGHER-ORDER MARKOV PROCESS INCORPORATING REVERSIONS EFFECTS.

The paper presents a formal approach which may increase the realism and parsimony of higher-order Markov models applied to certain human behaviors. Often in behavioral applications, any improvements in fit available from increasing the order of a Markov model would be more than offset by interpretive problems caused by the very rapid increase in the number of independent parameters. The model proposed here for the higher-order process greatly reduces the number of independent parameters, replacing them with sociologically relevant effects of persistence in and reversion to previous conditions. The general model is called the "reversion model." In it, individuals are allowed to carry along some information about their pasts, for a number of periods corresponding to the order of the model. The parameters describing residence histories are constructed to give each individual an underlying set of first-order transition probabilities, which are modified by experience of the various states of the system. When an individual occupies a particular state, his relative probability of future residence there (vis-a-vis the other states as a group) is permitted to change. But occupation of a particular state is not permitted to affect the relative chances of residence among the other states. With suitable constraints, the number of parameters of this higher-order process no longer increases geometrically with the order, but only arithmetically. Maximum likelihood estimation formulas are derived for the reversion model, which is then applied to longitudinal data on the work activities of U.S. Ph.D. physicists and chemists in 1960-1966, and is found to fit well using likelihood ratio tests. [ABSTRACT FROM AUTHOR]