Macroeconomic data consist mainly of the aggregate values of economic flows either at the level of the total economy, such as GDP and National Income, or at lower levels of aggregation such as the income, expenditure, and saving of the household or government sectors. The various flows are inter-related and must be defined and measured consistently with each other within an overall economic accounting framework. The internationally agreed System of National Accounts, or SNA, used by most countries in the world, is designed to provide such a framework. It is a complex system covering production, income distribution, consumption, capital formation, and financing for a hierarchy of sub-sectors and sectors up to the level of the economy as a whole. (T.P. Hill, in International Encyclopedia of the Social & Behavioral Sciences, 2001).