The study looked at how the prices and quality of Japanese cars have changed over time. They found that the official price index didn't accurately reflect the quality changes in cars. Quality-adjusted prices for cars actually went down slightly each year from 1990-94, even though the official price index went up. Different car sizes and styles also had different quality-adjusted prices. The current method used to adjust for quality changes in the price index didn't work well, but a new method called the hedonic approach did a better job.