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...

We examine the degree of natural gas market integration in Europe, North America and Japan, between the mid 1990's and 2002. The relationship between the international gas marker prices, and their relation to the oil price, are investigated through principal component analysis and Johansen...