The Price-Adjustment Equation

The price-adjustment equation tells us that when real GDP is below potential output, the output gap is positive, and the actual inflation rate is below its autonomous level. The opposite is true if real GDP is above potential output. The output gap matters for inflation because as GDP increases relative to potential output, labor and other inputs become scarcer. Firms see increasing costs and increase their prices as a consequence. The second term of the price adjustment equation shows that when real GDP is above potential output (the output gap is negative), there is upward pressure on prices in the economy. The inflation rate exceeds autonomous inflation. By contrast, when real GDP is below potential output (the output gap is negative), there is downward pressure on prices. The inflation rate is below the autonomous inflation rate. The “inflation sensitivity” tells us how responsive the inflation rate is to the output gap. If the output gap were the only factor affecting prices in the economy, then we would often expect to see deflation—decreasing prices. In particular, we would see deflation whenever the economy was in a recession. Although the United States and some other economies have occasionally experienced deflation, it is relatively rare. We can conclude that there must be factors other than the output gap that cause inflation to be positive. Autonomous inflation is the inflation rate that prevails in the economy when the economy is at potential output (the output gap is zero). In the United States in recent decades, the inflation rate has been positive but low, meaning that prices have been increasing on average but at a relatively slow rate. Autonomous inflation is typically positive because most economies have some growth of the overall money supply in the long run. A positive output gap then translates not into deflation but simply into an inflation rate below the level of autonomous inflation. Thus in the FOMC statement with which we opened this chapter, the discussion is not about how contractionary policy will cause deflation; it is about how this policy will moderate the inflation rate.