第2章宏观经济学的数据..ppt

* The next slide uses simple algebra to show that the CPI is a weighted average of prices; the weight on each price reflects that good’s relative importance in the CPI basket. The algebra is very similar to that of an earlier slide that showed that the GDP deflator is a weighted average of prices. * The formula for the GDP deflator is 100*NGDP/RGDP. It’s not obvious to most students that this is a measure of the average level of prices. But, using some simple algebra, this slide shows that the GDP deflator really is a weighted average of prices. Because this material might seem a bit more technical, and isn’t in the textbook, I have “hidden” this slide. If you wish to include it in your lecture, simply “unhide it” click on the “Slide Show” pull-down menu and unselect “hide slide”. Note: Because the weights don’t all sum to 1, the GDP deflator is a weighted sum, not a weighted average. * * * Since constant-price GDP is easier to understand and compute, and because the two measures of real GDP are so highly correlated, the chapter (and indeed the textbook) emphasizes the constant-price version of real GDP. However, if this topic is important to you and your students, you should have them carefully read page 23, and give them one or two exercises requiring students to computer or compare constant-price and chain-weighted real GDP. * Regarding the comparison of dollar figures from different years: If we want to know whether the average college graduate today is better off than the average college graduate of 1975, we can’t simply compare the nominal salaries, because the cost of living is so much higher now than in 1975. We can use the CPI to express the 1975 in “current dollars”, i.e. see what it would be worth at today’s prices. Also: when the price of oil (and hence gasoline) shot up in 2000, some in the news reported that oil prices were even higher than in the 1970s. This was true, but only in nominal terms. If you use the CPI to adju