Сравнение на методи

	Intervening Opportunities Model	Gravity Model of Migration
Област	Migration Studies	Human Geography
Семейство	Regression model	Regression model
Година на възникване	1940	1946
Създател	Samuel A. Stouffer	George Kingsley Zipf (formalized); analogy to Newton's law of gravitation
Тип	Spatial-interaction model of migration volume	Spatial-interaction regression model for migration flows
Основополагащ източник	Stouffer, S. A. (1940). Intervening Opportunities: A Theory Relating Mobility and Distance. American Sociological Review, 5(6), 845-867.	Zipf, G. K. (1946). The P1 P2 / D hypothesis: On the intercity movement of persons. American Sociological Review, 11(6), 677–686.
Други названия	Stouffer Intervening Opportunities, Opportunity-Based Migration Model, Law of Intervening Opportunities	Migration Gravity Model, Demographic Gravity Model, Zipf P1P2/D Model, Gravity Model of Spatial Interaction (Migration)
Свързани	3	4
Резюме	The intervening opportunities model, introduced by Samuel Stouffer in 1940, explains the volume of migration between two places not by the physical distance separating them but by the number of opportunities available at the destination relative to the opportunities a migrant would encounter along the way. Its central claim is provocative: there is no necessary relationship between mobility and distance. Distance only matters because crossing more of it usually means passing more chances to stop. Formally, the number of people moving a given distance is directly proportional to the number of opportunities at that distance and inversely proportional to the number of intervening opportunities. Stouffer revised the model in 1960 to add 'competing migrants' — rivals converging on the same destination from other origins — giving spatial-interaction analysis an alternative to the gravity model that is grounded in opportunity structure rather than mass and distance.	The gravity model of migration explains the volume of movement between two places as proportional to the product of their populations (masses) and inversely proportional to the distance separating them, by direct analogy to Newton's law of universal gravitation. Formalized for intercity movement by George Kingsley Zipf in 1946 and embedded in regional science by Walter Isard, it is the workhorse model of human geography for predicting migration, commuting, and other spatial-interaction flows.