The Phillips curve, which shows the relationship between inflation and unemployment, was changed by Friedman and Phelps in the 1960s. They said that in the long run, unemployment will be at a natural rate, and in the short run, it will go up if unemployment is forced below this rate. However, this approach assumes that the job market always balances out and that changes in unemployment only happen when workers or companies are tricked. A better way to explain this is by looking at how prices and wages change slowly. In the 1970s and 1990s, inflation and unemployment were linked because of how demand and supply work together. But in recent years, inflation hasn't responded much to high or low unemployment.