Push-Pull Factor Analysis

Intervening obstacles are the barriers that lie between origin and destination and must be overcome for a move to occur regardless of how attractive the destination is — physical distance, transport cost, legal restrictions, and borders being the classic examples. In Lee's scheme they form a separate term from the place factors: even a large net pull will not produce migration if the obstacles are prohibitive, and lowering obstacles can release flows that latent push-pull differentials had already created. Treating obstacles as a distinct screen, rather than folding them into a distance variable, is what distinguishes Lee's full framework, and it is the seed of the related intervening-obstacles analysis.

Lee emphasized that origin and destination factors carry a plus, minus, or zero whose sign depends on the individual evaluating them. A cold climate may repel one resident and attract another who prefers it; abundant farmland pulls a would-be farmer and means nothing to an aspiring office worker. Because valence is person-specific, aggregate push-pull accounts describe the dominant tendencies of a population rather than a universal calculus. This heterogeneity is precisely why the framework treats personal factors as a fourth element and why it explains selectivity in who migrates rather than only the total volume.

It sits between the two. Lee derived testable hypotheses about migration volume, streams and counter-streams, and selectivity, so it is more than a bare taxonomy. But as Massey and colleagues argue, it lacks an explicit model of how individuals optimize, which is why neoclassical economics and the new economics of labor migration are often used to supply the behavioral mechanism the framework leaves implicit. In contemporary practice push-pull is best treated as a comprehensive organizing scaffold that frames the question, with a more specific theory recruited to explain the decision once the relevant factors are inventoried.