Publications

The CAPM model assumes stock returns to be a linear function of the market return. However, there is considerable evidence that the beta stability assumption commonly used when estimating the model is invalid. Nonparametric regression methods are used to examine the stability of beta coefficients in German stock returns. Since local polynomial regression is used for estimation, known methods for testing the stability and for bandwidth choice can be used. For some returns the test indicates time-varying betas. For these returns conditionally parametric fits are calculated.

The huge difference in the level and variance of student performance in the 2000 PISA study between Finland and Germany motivates this paper. It analyses why Finnish students performed so much better by estimating educational production functions for both countries. The difference in the reading proficiency scores is assigned to different effects, using Oaxaca-Blinder and Juhn-Murphy-Pierce decomposition techniques. The analysis shows that German students have on average a more favorable background except for the lowest deciles, but experience much lower returns to these background characteristics in terms of test scores than Finnish students. The results imply that early streaming in Germany penalizes students in lower school types and leads to a greater inequality of educational achievement. It remains unclear, however, if this can be attributed to the effect of school types per se or student background and innate ability that determine the allocation process of students into school types. Overall, the variation in test scores can be explained much better by the observable characteristics in Germany than in Finland.

For a bivariate data set the dependence structure can not only be measured globally, for example with the Bravais-Pearson correlation coefficient, but the dependence structure can also be analyzed locally. In this article the exploration of dependencies in the tails of the bivariate distribution is discussed. For this a graphical method which is called chi-plot and which was introduced by Fisher and Switzer (1985, 2001) is used. Examples with simulated data sets illustrate that the chi-plot is suitable for the exploration of dependencies. This graphical method is then used to examine stock-return pairs. The kind of tail-dependence between returns has consequences, for example, for the calculation of the Value at Risk and should be modelled carefully. The application of the chi-plot to various daily stock-return pairs shows that different dependence structures can be found. This graph can therefore be an interesting aid for the modelling of returns.

This paper analysis the robustness of the causal relationship between schooling
and wages. Different estimators and instruments are compared under the
assumption of heterogeneous returns to schooling. A data set from Germany is
employed. It is shown that the results depend crucially on the choice of
instruments and not so much on the applied estimator.

The current study integrates the repeated game approach to implicit contracts and the analysis of explicit bonus rules based on subjective performance evaluation to determine the optimal structure of the compensation scheme for the average white-collar employee. In contrast to previous contributions we assume that the agent is risk-neutral but liquidity constrained. The salary reflects the maximum reward associated with contractual compliance which can be implicitly agreed. If the probability that the employee remains within the firm increases, the principal can reduce the rent captured by the agent. Hence, the optimal salary increases and the explicit bonus decreases. Nevertheless, the optimal effort supply unambiguously increases.

The current study investigates a tripartite incentive contract between an innovator supplying an intellectual asset, a professional assigned to productive tasks, and a consulting firm specialized in recruiting qualified personnel. The liquidity-constrained professional is compensated by receiving a share of one half in the new venture. With continuous search activities of the consultant the pure tripartite partnership implements the consultant s expected profit maximum. The consultant s and the innovator s shares reflect the relative value of search. However, the consultant s optimal search effort is inefficiently low. With binary search and only two innovator types , there may also exist bipartite partnerships of equals between the innovator and the professional, and bipartite partnerships of equals between the consultant and the professional. The latter emerge from complete buy-outs of innovators with low value business ideas.

Unter dem Stichwort Patchwork-Biografien wird die Tatsache, dass ein großer Teil der abhängig Beschäftigten ihren erlernten Beruf nicht mehr ausüben, in jüngster Zeit viel diskutiert. Diese Studie liefert einen empirischen Beitrag zur Anatomie des Berufswechsel für westdeutsche Männer auf Basis der BIBB/IAB-Daten 1998/1999. Als Grundlage für die empirische Analyse wird ein theoretisches Modell der Wahl zwischen horizontal differenzierten Berufen entwickelt. Die wichtigsten Ergebnisse sind: Ex post beobachtete Berufswechsel hängen negativ vom Durchschnittslohn im Ausbildungsberuf und positiv vom Durchschnittslohn im Erwerbsberuf ab. Der deskriptiv beobachtete durchschnittliche Entlohnungseffekt eines Berufswechsels ist signifikant positiv, verstärkt sich noch, wenn für den Ausbildungsberuf kontrolliert wird, und ist demgegenüber signifikant negativ, wenn für den Erwerbsberuf kontrolliert wird. Der geschätzte kausale durchschnittliche Entlohnungseffekt ist positiv. Die Ergebnisse sind insgesamt damit konsistent, dass Berufswechsel vor allem damit zusammenhängen, dass Beschäftigte im neuen Erwerbsberuf größere Verdienst- und Karrierechancen wahrnehmen können.

This paper investigates the effect of reforms on the time-to-degree and attendance at colleges. My model predicts that with imperfect credit markets imposing tuition fees may raise instead of reducing the time-to-degree. In the final section of the paper, I present a proposal for a reform which incorporates differentiated fees and a credit point system. I derive an optimal fee for maximal attendance in higher education.