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.