【正文】 Willingness to pay measures marginal benefit. Demand 169。 2020 Pearson AddisonWesley A Change in Demand When some influence on buying plans other than the price of the good changes, there is a change in demand for that good. The quantity of the good that people plan to buy changes at each and every price, so there is a new demand curve. When demand increases, the demand curve shifts rightward. When demand decreases, the demand curve shifts leftward. Demand 169。 2020 Pearson AddisonWesley Six main factors that change demand are ? The prices of related goods ? Expected future prices ? Ine ? Expected future ine and credit ? Population ? Preferences Demand 169。 2020 Pearson AddisonWesley Prices of Related Goods A substitute is a good that can be used in place of another good. A plement is a good that is used in conjunction with another good. When the price of substitute for an energy bar rises or when the price of a plement of an energy bar falls, the demand for energy bars increases. Demand 169。 2020 Pearson AddisonWesley Expected Future Prices If the expected future price of a good rises, current demand for the good increases and the demand curve shifts rightward. Ine When ine increases, consumers buy more of most goods and the demand curve shifts rightward. A normal good is one for which demand increases as ine increases. An inferior good is a good for which demand decreases as ine increases. Demand 169。 2020 Pearson AddisonWesley Expected Future Ine and Credit When expected future ine increases or when credit is easy to obtain, the demand might increase now. Population The larger the population, the greater is the demand for all goods. Preferences People with the same ine have different demands if they have different preferences. Demand 169。 2020 Pearson AddisonWesley Figure shows an increase in demand. Because an energy bar is a normal good, an increase in ine increases the demand for energy bars. Demand 169。 2020 Pearson AddisonWesley A Change in the Quantity Demanded Versus a Change in Demand Figure illustrates the distinction between a change in demand and a change in the quantity demanded. Demand 169。 2020 Pearson AddisonWesley Movement Along the Demand Curve When the price of the good changes and everything else remains the same, the quantity demanded changes and there is a movement along the demand curve. Demand 169。 2020 Pearson AddisonWesley A Shift of the Demand Curve If the price remains the same but one of the other influences on buyers’ plans changes, demand changes and the demand curve shifts. Demand 169。 2020 Pearson AddisonWesley If a firm supplies a good or service, then the firm 1. Has the resources and the technology to produce it, 2. Can profit from producing it, and 3. Has made a definite plan to produce and sell it. Resources and technology determine what it is possible to produce. Supply reflects a decision about which technologically feasible items to produce. The quantity supplied of a good or service is the