This paper compares the simple Markov process commonly used in migration studies with an economic model of migration where interregional wage differences are the equilibrating variables. Using the economic model, it appears unlikely that regional exit and entry rates will remain stable as the population is redistributed. As a result, both theory and empirical interstate migration evidence suggest that Markov migration projections will usually understate the population changes required before stochastic equilibrium is reached. IN RECENT YEARS the social sciences, and particularly economics, have experienced

I. Introduction and summary of main conclusions, 491. — II. The structure of an aggregate economy, 493. — III. The general saving function and the existence of the steady-state growth path, 494. — IV. Uniqueness and stability of the steady-state growth path, 498.