Equilibrium

Earlier we have examined the demand decisions of buyers and the supply decisions of sellers, separately. However, in the market for any particular good, the decisions of buyers interact simultaneously with the decisions of sellers. When the demand for a good equals the supply of the good, the market for the good is said to be in equilibrium. Associated with the market equilibrium will be an equilibrium quantity and an equilibrium price.

Elasticity

In addition to understanding how equilibrium prices and quantities change as demand and supply change, economists are also interested in understanding how demand and supply change in response to changes in prices and incomes. The responsiveness of demand and supply to changes in prices or incomes is measured by the elasticity of demand or supply.

If the percentage change in quantity demanded is greater than the percentage change in price, demand is said to be price elastic, or very responsive to price changes. If the percentage change in quantity demanded is less than the percentage change in price, demand is said to be price inelastic, or not very responsive to price change. Similarly, supply is price elastic when the percentage change in quantity supplied is greater than the percentage change in price, and supply is price inelastic when the percentage change in quantity supplied is less than the percentage change in price. The price elasticity of demand or supply will differ among goods.

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GDP, INFLATION, AND UNEMPLOYMENT

The branch of economics known as macroeconomics examines the aggregate performance of all markets in the market system. In studying macroeconomic behavior, economists rely on several statistics that measure the performance of the macroeconomy. The three most commonly used measures of macroeconomic performance are the gross domestic product (GDP), the rate of inflation, and the unemployment rate.

GDP

GDP is defined as the market value of all final goods and services produced domestically in a single year and is the single most important measure of macroeconomic performance. A related measure of the economy's total output is gross national product (GNP), which is the market value of all final goods and services produced by a nation in a single year.