must be satisfied for the efficient use of resources, as first demonstrated by the Italian economist Enrico Barone. Economists believe that incentives and costs play a pervasive role in shaping decision making. An immediate example of this is the consumer theory of individual demand, which isolates how prices (as costs) and income affect quantity demanded. Modern mainstream economics has foundations in neoclassical economics, which began to develop in the late 19th century. Mainstream economics also acknowledges the existence of market failure and insights from Keynesian economics, most contemporaneously in the macroeconomic new neoclassical synthesis. It uses models of economic growth for analyzing long-run variables affecting national income. It employs game theory for modeling market or non-market behavior. Some important insights on collective behavior (for example, emergence of organizations) have been incorporated through the new institutional economics. A definition that captures much of modern economics is that of Lionel Robbins in a 1932 essay: "the science which studies human behaviour as a relationship between ends and scarce means which have alternative uses." Scarcity means that available resources are insufficient to satisfy all wants and needs. Absent scarcity and alternative uses of available resources, there is no economic problem. The subject thus defined involves the study of choice, as affected by incentives and resources. Mainstream economics encompasses a wide (but not unbounded) range of views. Politically, most mainstream economists hold views ranging from laissez-faire to modern liberalism. There are also differing views on certain empirical claims within macroeconomics, such as the effectiveness of expansionary fiscal policy under certain conditions. Disputes within mainstream macroeconomics tend to be characterised by disagreement over the convincingness of individual empirical claims (such as the predictive power of a specific model) and in this respect differ from the more fundamental conflicts over methodology that characterised previous periods (like those between Monetarists and Neo-Keynesians), in which economists of differing schools would disagree on whether a given work was even a legitimate contribution to the field. Contemporary heterodox economics In the late 19th century, a number of heterodox schools contended with the neoclassical school that arose following the marginal revolution. Most survive to the present day as self-consciously dissident schools, but with greatly diminished size and influence relative to mainstream economics. The most significant are Institutional economics, Marxian economics and the Austrian School. The development of Keynesian economics was a substantial challenge to the dominant neoclassical school of economics. Keynesian