Ethnic fragmentation is a variable increasingly used in the economic literature to explain differences in economic development level, growth or the incidence of conflicts. Nearly all articles have in common that they treat ethnic fragmentation as a static, exogenous fact. Only recently some...

In this paper we show that findings of an apparently instable popularity function of U.S. presidents, as reported in the previous literature, are likely the consequence of the common use of linear estimation techniques. Employing Penalized Spline Smoothing in the context of Additive Mixed Models...