The Short-Run Trade off Between Inflation and Unemployment
Consider the options the Phillips curve gives to a policy maker who can influence aggregate demand with monetary or fiscal policy.
At any moment, expected inflation and supply shocks are beyond the policy maker’s immediate control.
Yet, by changing aggregate demand, the policy maker can alter output, unemployment, and inflation.
The policymaker can expand aggregate demand to lower unemployment and raise inflation.
Or the policymaker can depress aggregate demand to raise unemployment and lower inflation.
Figure 13-4 plots the Phillips curve equation and shows the short-run trade off between inflation and unemployment.
When unemployment is at its natural rate (u un), inflation depends on expected inflation and the supply shock (p
Ep u).
The parameter b determines the slope of the trade off between inflation and unemployment.
In the short run, for a given level of expected inflation, policy makers can manipulate aggregate demand to choose any combination of inflation and unemployment on this curve, called the short-run Phillips curve.
Notice that the position of the short-run Phillips curve depends on the expected rate of inflation.
If expected inflation rises, the curve shifts upward,and the policy maker’s trade off becomes less favorable:
inflation is higher for any level of unemployment. Figure 13-5 shows how the trade off depends on expected inflation.
Because people adjust their expectations of inflation over time, the trade off between inflation and unemployment holds only in the short run. The policymaker cannot keep inflation above expected inflation (and thus unemployment below its natural rate) forever.
Eventually, expectations adapt to whatever inflation rate the policy maker has chosen.
In the long run, the classical dichotomy holds, unemployment returns to its natural rate, and there is no tradeoff between inflation and unemployment.