The study looked at how inflation in the US has behaved since 1985. They found that inflation can be predicted by looking at how much people expect prices to rise and how many people are unemployed in the short term. In the late 1990s, people started to expect prices to rise at a steady rate, which changed how inflation and unemployment are related. This is why high unemployment during the Great Recession didn't lower inflation much - people expected prices to keep rising, and short-term unemployment didn't rise as much as total unemployment.