3 A Multitude of大量)Models No one model can address all the issues we care about. For example, If we want to know how a fall in aggregate income affects new car prices,we can use the S/D model for new cars. But if we want to know why aggregate income falls, we need a different model. CHAPTER1 The Science of Macroeconomics slide 24CHAPTER 1 The Science of Macroeconomics slide 24 A Multitude of(大量)Models No one model can address all the issues we care about. For example, ▪ If we want to know how a fall in aggregate income affects new car prices, we can use the S/D model for new cars. ▪ But if we want to know why aggregate income falls, we need a different model. 3