Outside the model. For instance, in traditional Neo-classical economics, models of growth rely on an exogenous factor. To keep growing, an eco¬nomy needs continual infusions of technological progress. Yet this is a force that the neo-classical model makes no attempt to explain. The rate of technological progress comes from outside the model; it is simply assumed by the economic modelers. In other words, it is exogenous. New growth theory tries to calculate the rate of technological progress inside the economic model by mapping its relationship to factors such as human capital, free markets, competition and government expenditure. Thus, in these models, growth is ¬endogenous.