The difference between the short- and longrun Phillips curves, which is now a staple of textbooks, was developed by Milton Friedman and Edmund Phelps, and the effect of making expectations rational or model consistent was emphasized by Robert Lucas, whose islands model provided an imperfect information reason for a nonvertical short-run Phillips curve.
In Okun’s law, the Okun coefficient – the coefficient specifying how much a change in the unemployment rate affects output – appears to have declined over time. So has the trend rate of productivity growth, which is a critical determinant of future levels of per capita income.