Is the Phillips Curve of Germany Spurious?

A simple plot of seasonal adjusted quarterly data between the change of nominal wage rates and the unemployment rate for the German economy shows a picture similar to that by which Phillips was inspired to his famous discovery, that there is a long-term tendency of a negative, non-linear relationship coupled with minor deviations from this tendency, which form so-called loops. At first sight, the Phillips Curve of Germany comprises clusters of data points and movements between these clusters. In spite of the striking differences of these phenomena, a model with one regression equation is sufficient to explain the loops, the movements between the loops and the long-term tendency of the German Phillips Curve. It might well be that the German Phillips Curve and the corresponding regressions are spurious, but an allegedly missing co-integration of wage rate changes and unemployment rate is not the argument that could be drawn on to sustain this scepticism. On the contrary, both variables are co-integrated. To get a more detailed insight into the relationship, the two variables are split into a trend and a cyclical component by the help of the HP-filter. The results of regression analyses applied to the separated components support Phillips’ hypothesis of a negative relationship between wage rate changes and the unemployment rate.