The growth portion of the goods and services module responds to endogenous labor supply growth (from the demographic model), endogenous capital stock growth (with a variety of influences on the investment level), and a mixture of endogenous and exogenous specification of advance in multifactor productivity (MFP). The endogenous portion of MFP represents a combination of convergence and country-specific elements that together create a conditional convergence formulation.
The equilibrium-seeking portion of the goods and services market module uses increases or decreases in inventories and prices (by sector) to balance demand and supply. Inventory stocks in each sector serve as buffers to reconcile demand and supply temporarily. Prices respond to stock levels. The central equilibrium problem that the module must address is maintaining domestic and global balance between supply and demand in each of the sectors of the model. IFs relies on three principal mechanisms to assure equilibrium in each sector: (1) price-driven changes in domestic demand; (2) price-driven changes in trade (IFs represents trade and global financial flows in pooled rather than bilateral form); and (3) stock-driven changes in investment by destination (changes in investment patterns could also be price-driven, but IFs uses stocks because of its recursive structure, so as to avoid a 2-year time delay in the response of investment).
The economic model makes no attempt through iteration or simultaneous solution to obtain exact equilibrium in any time point. In addition to being observationally obvious, Kornai (1971) and others have, of course, argued that real world economic systems are not in exact equilibrium at any time point, in spite of the convenience of such assumptions for much of economic analysis. Similarly, the SARUM global model (Systems Analysis Research Unit 1977) and GLOBUS (Hughes 1987) used buffer systems similar to that of IFs with the model "chasing" equilibrium over time.
Two "physical" or "commodity" models in IFs, agriculture and energy, have structures very similar to each other and to the economic model. They have partial equilibrium structures that optionally, and in the normal base case, replace the more simplified sectoral calculations of the goods and services market module.
The goods and services market sits within a larger social accounting matrix that tracks financial flows among households, firms, and the government. The integrated economic model also allows computation of income distribution and poverty rates.
For help understanding the equations see Equation Notation.
- The Goods and Services Market
- The Social Accounting Matrix (SAM)
- The Adjustment Mechanism and Other Specialized Functions
- Creating and Initializing Country SAMS: The Pre-processor