Gravity model of trade
The gravity model of trade in international economics is a model that, in its traditional form, predicts bilateral trade flows based on the economic sizes and distance between two units. Research shows that there is "overwhelming evidence that trade tends to fall with distance." The model was first introduced by Walter Isard in 1954, who elaborated the concept of "income potential" within the framework of international economics, building upon John Quincy Stewart's earlier idea of demographic gravitation, which had been introduced in 1941.