The Unassuming Economist

From an article by Christopher G. Collins (PIIE) and Joseph E. Gagnon (PIIE):

“The US economy is running hot, with a record high rate of job vacancies and the lowest unemployment rate in nearly fifty years. Yet most forecasters predict no increase at all in inflation. This combination appears to challenge the validity of the Phillips curve, a popular economic model dating from the 1950s that predicts rising inflation when unemployment is low and falling inflation when unemployment is high. In a new paper, however, we show that the relationship between inflation and unemployment has shifted twice—in the late 1960s and in the mid-1990s. The paper replicates the findings of some other researchers, who find a very flat Phillips curve since the 1990s, implying that unemployment has little effect on inflation. But we also propose an alternative hypothesis: The Phillips curve is bent when inflation is low so that high unemployment has little downward effect on inflation, but low unemployment still pushes inflation up. If we are right, inflation is likely to rise modestly over the next couple of years. We will explore what this means for monetary policy in a subsequent post.

THE EVOLVING US PHILLIPS CURVE

Alban Phillips (1958) developed the original curve bearing his name. It related the rate of wage inflation to the unemployment rate in the United Kingdom over the period 1861–1913. Olivier Blanchard (2017, chapter 8) showed that a similar downward-sloping curve in terms of price inflation and unemployment was apparent in the United States in 1900–1960. Our paper confirms Blanchard’s finding that the rising inflation of the late 1960s led to the unmooring of expectations of inflation from the stable low levels that had prevailed before then and a shift in the Phillips curve to a relationship between the change in the rate of inflation and the unemployment rate. The return of inflation to a very low and stable level led to a second shift in the Phillips curve in the mid-1990s, back to a relationship between the level of inflation and the unemployment rate.

In addition to this shift in the persistence of inflation, many researchers have found that the Phillips curve has been very flat since the 1990s, so that changes in unemployment have little effect on inflation. This was most dramatically demonstrated in the aftermath of the Great Recession of 2008–09, when unemployment remained very high for years and yet inflation barely dipped. We show, however, that another hypothesis fits the data equally well: The Phillips curve may become bent when inflation is low, with a flat portion for high unemployment and a steeper portion for low unemployment.”

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