An assumption often added to the rational choice paradigm is that individual preferences are self-interested, in which case the individual can be referred to as a homo economicus. Such an individual acts "as if" balancing costs against benefits to arrive at action that maximizes personal advantage. Proponents of such models, particularly those associated with the Chicago school of economics, do not claim that a model's assumptions are an accurate description of reality, only that they help formulate clear and falsifiable hypotheses. In this view, the only way to judge the success of a hypothesis is empirical tests. To use an example from Milton Friedman, if a theory that says that the behavior of the leaves of a tree is explained by their rationality passes the empirical test, it is seen as successful.