The study looked at how different factors affect the US economy over time. They found that there are four main types of shocks that impact the economy: supply, demand, monetary policy, and fiscal policy. Supply shocks mainly affect GDP, while demand shocks impact employment and inflation. Both monetary and fiscal policies have significant effects on output and prices, and they are used to counteract demand shocks. Interestingly, negative demand shocks can actually lead to long-term improvements in productivity.