by Calculated Risk on 1/30/2012 07:28:00 PM

The average duration of unemployment in the US increased sharply during the recent recession, and was still near the record high in December. One of the reasons the average has stayed high is because of a change in the measurement methodology, but even after accounting for that change, the duration is still near record levels.

Another measure - the median duration of unemployment - has declined slightly from a peak of 25 weeks in June 2010, to 21 weeks in December 2011. In the severe recession of the early '80s, the median duration peaked at 12.3 weeks, even though the unemployment rate was higher in the early '80s than during the recent employment recession.

Researchers Rob Valletta and Katherine Kuang at the San Francisco Fed look at the reasons the duration increased: Why Is Unemployment Duration So Long?

During the recent recession, unemployment duration reached levels well above those of past downturns. Duration has continued to rise during the uneven economic recovery that began in mid-2009. Elevated duration reflects such factors as changes in survey measurement, the demographic characteristics of the unemployed, and the availability of extended unemployment benefits. But the key explanation is the severe and persistent weakness in aggregate demand for labor.

This seems obvious, but it is important for policymakers to understand that the primary cause of the increase in duration is not extended unemployment benefits or changes in demographics, but weak aggregate demand.