text: Jan Tinbergen developed a model for this phenomenon which uses an equation similar to the law of universal gravitation to predict its amount.
full_question: Jan Tinbergen developed a model for this phenomenon which uses an equation similar to the law of universal gravitation to predict its amount. Another model of this phenomenon assumes that labor is the only variable factor. Paul Samuelson outlined a modification to a model of this phenomenon that uses a 2x2x2 (2 by 2 by 2) model that allows for variances in both capital and labor. Paul Krugman was awarded the Nobel Prize for his work in this area, which is described by the (*) Heckscher-Ohlin Model. The most basic model that claims every country should produce what it is best at was developed by David Ricardo and is called comparative advantage. For 10 points, name this phenomenon, which can be controlled by the application of tariffs, where two countries exchange goods and services.
first_sentence: Jan Tinbergen developed a model for this phenomenon which uses an equation similar to the law of universal gravitation to predict its amount.
raw_answer: international trade