phillips curve_laffer curve_phillips curve公式(3)

The real wage is restored to its old level, and the unemployment rate returns to the natural rate。 But the price inflation and wage inflation brought on by expansionary policies continue at the new, higher rates。

Friedman’s and Phelps’s yses provide a distinction between the “short-run” and “long-run” Phillips curves。 So long as the average rate of inflation remains fairly constant, as it did in the 1960s, inflation and unemployment will be inversely related。 But if the average rate of inflation changes, as it will when policymakers persistently try to push unemployment below the natural rate, after a period of adjustment, unemployment will return to the natural rate。 That is, once workers’ expectations of price inflation have had time to adjust, the natural rate of unemployment is compatible with any rate of inflation。

The long-run Phillips curve could be shown on as a vertical line above the natural rate。 The original curve would then apply only to brief, transitional periods and would shift with any persistent change in the average rate of inflation。 These long-run and short-run relations can be combined in a single “expectations-augmented” Phillips curve。 The more quickly workers’ expectations of price inflation adapt to changes in the actual rate of inflation, the more quickly unemployment will return to the natural rate, and the less successful the government will be in reducing unemployment through monetary and fiscal policies。

The 1970s provided striking confirmation of Friedman’s and Phelps’s fundamental point. Contrary to the original Phillips curve, when the average inflation rate rose from about 2.5 percent in the 1960s to about 7 percent in the 1970s, the unemployment rate not only did not fall, it actually rose from about 4 percent to above 6 percent.

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