Explain the error in this interpretation of inflation data:

In the 12-month period ending in December of 1980, consumer prices rose by 12.4 percent—after a 13.3 percent increase the year before. Similar measures of inflation over the next three years were 8.9 percent, 3.9 percent, and 3.8 percent…. We are certainly paying less for what we buy now than we were at the end of [1980].