Good accounting turns data into information. National income accounting is studied for two reasons. First, the national income accounts provide the formal structure for macrotheory models. Output is divided in two ways. On the production side, output is paid out to labor in the form of wages and to capital in the form of interest and dividends. On the demand side, output is consumed or invested for the future. The division of output into factor payments (wages, etc.) on the production side provides a framework for study of growth and aggregate supply. The division of income into consumption, investment, and so on, on the demand side provides the framework for studying aggregate demand. The input and output, or demand and production, accountings are necessarily equal in equilibrium. In addition to looking at real output, the national income accounts include measures of the overall price level. This provides a basis for discussions of inflation. The second reason for studying national income accounts is to learn a few ballpark numbers that help characterize the economy. While memorizing exact statistics is a waste of time, knowing rough magnitudes is vital for linking theory to the real world (Dornbusch,. et al., 2011). The rules of national income accounting include several important identities. An identity is an equation that must be true because of the way the variables in the equation are defined. Identities are useful to keep in mind, for they clarify how different variables are related to one another (Mankiw, 2004).