Like Paul Krugman, Justin Wolfers also wrote yesterday about my blog post of January 14 on the correlation between investment and unemployment. Wolfers argues that the relationship did not exist in earlier years. He is wrong.
His argument is based on the observation that the scatter of points for the 1990-2010 period, shown in one of my graphs, shifts up and to the right—higher unemployment for a given level of investment—if you include the 1970s and 1980s. The scatter of points shift back down and to the left if you go back further. This shift up in unemployment in the 1970s and 1980s was due in part to the well-documented longer term increase in the natural rate of unemployment in the 1970s and 1980s, which many macroeconomists have researched and written about, but which Wolfers does not mention. When you recognize that such longer-term historical trends exist, you can see that there is a strong correlation between investment and unemployment that goes back before 1990.