Research: Natural Rate of Unemployment under 5% and Falling

From the Chicago Fed: Changing labor force composition and the natural rate of unemployment Excerpts:

We estimate our baseline natural rate of unemployment as of 2014:Q4 to be 4.9% —0.5 percentage points lower than the CBO’s estimate of the short-run natural rate. We project this rate to fall by about 0.06 percentage points per year through the end of the decade, reaching 4.5% at the end of 2020—0.7 percentage points below the CBO’s estimate.

Two broad assumptions underlie these simple calculations. First, demographics and educational attainment are fundamental determinants of unemployment, and thus, changes in them over time should drive overall levels of aggregate unemployment. Second, the unemployment rate was at its natural rate in late 2005. Both of these assumptions seem plausible, but neither is completely unassailable. ...
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While great progress has been made over the past few years, significant labor market slack remains. We estimate the natural rate at or below 5%, at least half of a percentage point below its actual level as of March 2015. This estimate of slack, in combination with labor market measures such as LFP and involuntary part-time workers, may help explain why wage inflation and price inflation remain so low. Moreover, we estimate that absent major new developments, demographic and educational changes will persist, potentially reducing the trend unemployment rate to around 4.4% to 4.8% by 2020.