1. For the record. Larry Summers and I indeed argued for hysteresis in Europe in the 1980s. We thought, and I still do, that, in that context, high actual unemployment had led to an increase in the natural rate, and a strong expansion might reverse the effect.

2. I returned to the issue in the 2010s, first with Larry, and then alone in a JEP paper in 2018, looking at the evidence from 22 economies over the last 50 years . https://www.aeaweb.org/articles?id=10.1257/jep.32.1.97

3. I concluded that the evidence for hysteresis, either through scarring in the labor market, or through the effect of recessions on technological progress, was probably there but was not overwhelming.

4. Whatever your prior, pro or against, you were likely to come out of having looked at the data with a rather similar posterior… I see people citing it in strong support of the hypothesis; they should read the paper.

5. My belief at this point. There are surely instances of permanent effects of recessions or expansions, on individual behavior or on technology. Whether they add up to a significant macro effect is far from sure. I would not build a program based on a strong hysteresis effect.