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a = 0.2 |
a = 0.8 |
a = 1.1 |
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Columns generated with equations: Output gap = (output last year - equilibrium output)/equilibrium output; |
Why should prices be sticky? Production lags are one reason. Producers may need time to adjust output to a new level of prices. Another reason for price stickiness is that changes in prices can be costly to make. This reason makes sense if we interpret curves in the graph above as an aggregate supply and aggregate demand curves. Price changes irritate customers and reprinting price lists may be expensive.
The adjustment process yields more intriguing results if it depends not just on the pressure from the output gap, but also on past price movements. If a firm has seen the price of its products rising by 10% each period, it may expect prices to rise 10% in the next period and may base its pricing decisions not only on the output gap but also on this expected rate of inflation. We will call this additional force the expected rate of inflation, and for simplicity assume that it is equal to last period's rate of price change. The impact of this expected inflation will depend on how much people carry forward past inflation when setting future prices. If people expect inflation to be 10%, they may carry forward all of expected price change and mark up prices by the full 10%, or they may carry forward only part of it, or maybe none of it.
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Columns generated as in the previous table
except price level now is: |
In the table above, the current price depends on old price, on output gap with price stickiness, and on expected rate of inflation with the carry-forward factor. Adding effects from expected inflation gives the adjustment process a momentum that makes it overshoot equilibrium and results in a cycle. With extreme values, we can have the model completely unstable, so it will crash to zero or shoot off to infinity.
We have shown that simple models can generate cyclical adjustment processes. The keys are that some parts of the system stick, and that the past influences the future with a lag. If real-world economies adjust in similar ways, and it is not far-fetched to assume that they do, we may sometimes see cycles. Do not believe that cycles are forever buried in the graveyard of economic ideas.