(2017), “Should we reject the natural rate hypothesis?”, Peterson Institute for International Economics Working Paper, 17–14, November. 2 See for example, Ball, L. (2009) “Hysteresis in Unemployment: Old and New Evidence”, NBER Working Paper  No 14818; and Holzer, H. J., S. Raphael and M. A. Stoll (2006),"Employers in the Boom: How Did the Hiring of Less-Skilled Workers Change during the 1990s?
", Review of Economics and Statistics, Vol. 88 (May), pp. 283– 99. 3 See Blanchard, O. (2017,op.cit.). 4 A third broad explanation could be related to the type of shock hitting the economy. For instance, it could be the  case that favourable supply shocks were predominantly pushing output higher while keeping inflation in check in recent years.