text: Incorporating the concept of increasing returns to scale is the key element of the "new" theory of this activity.
full_question: Incorporating the concept of increasing returns to scale is the key element of the "new" theory of this activity. The Leontief paradox undermined attempts to model this activity, which Paul Samuelson predicted to lead to factor price equalization. The Heckscher-Ohlin model predicts the patterns of this activity based on capital and labor. David Ricardo described a principle stating that two entities may achieve gains from this activity if they each have a comparative advantage at producing goods. For 10 points, name this activity that is the exchange of goods or services between parties.
first_sentence: Incorporating the concept of increasing returns to scale is the key element of the "new" theory of this activity.
raw_answer: trade [or exchange until it is read]