The current attention to the relationship between inflation and economic slack has led to an intense debate on the stability of the Phillips curve and its power to explain the twin puzzle. Empirical research, especially in the United States, shows that the slope of the Phillips curve has varied over time, with a clear tendency to flatten over the years.
For the euro area, the evidence from several recent papers points to a steepening in recent years (see e.g. Oinonen and Paloviita (2014), Riggi and Venditti (2015) and Foroni and Porqueddu (2015)).