Triangulation: Validity and empirically-based hypothesis construction

The essay focuses on the opportunities and strengths of a multi-method approach, widely called methodological triangulation, in which different investigative methods are applied to one research object. In practice, this can be realized with the coupling of quantitative structural data concerning the life course and the interpretation and evaluation of life course data collected with qualitative methods. This approach is examined in order to shed light on the problem that research findings often show different phenomena and not the different aspects of one phenomenon. The discussion of the relationships of the findings to one another (congruent, complementary or divergent) shows that in this context a multi-method approach can nevertheless be used to increase validity and to test hypotheses. Further, its particular strengths are the empirically induced modification of existing models and theories, as well as the development of new explanations.     

An efficient nonparametric estimator for models with nonlinear dependence

We provide a convenient econometric framework for the analysis of nonlinear dependence in financial applications. We introduce models with constrained nonparametric dependence, which specify the conditional distribution or the copula in terms of a one-dimensional functional parameter. Our approach is intermediate between standard parametric specifications (which are in general too restrictive) and the fully unrestricted approach (which suffers from the curse of dimensionality). We introduce a nonparametric estimator defined by minimizing a chi-square distance between the constrained densities in the family and an unconstrained kernel estimator of the density. We derive the nonparametric efficiency bound for linear forms and show that the minimum chi-square estimator is nonparametrically efficient for linear forms.     

Pitfalls of Normal-Gamma Stochastic Frontier Models

Although conceptually pleasing, normal-gamma frontier models lead to difficult estimation problems. It is shown here that unless the sample size reaches several thousands of observations the shape parameter of the gamma density is hard to estimate, and that this carries over to estimates of the stochastic frontier, the individual inefficiencies, and the allocation of the overall variance to the stochastic frontier and to the inefficiencies.     

The topography of metropolitan employment: Identifying centers of employment in a polycentric urban area

While it is well recognized that US metropolitan areas are polycentric, there is little consensus as to the appropriate method for identifying concentrations of employment within them. Existing methods suffer from strong assumptions about parametric form, misspecification, or reliance on local knowledge to calibrate model parameters. This paper introduces a new nonparametric method for identifying subcenters. Results indicate that this, more flexible, nonparametric approach yields greater accuracy with regard to both urban and suburban centers compared with other approaches. This approach should provide better data for the numerous topics that depend on the spatial accounting of employment within metropolitan areas.     

Convergence in West German Regional Unemployment Rates

Abstract. Differences in regional unemployment rates are often used to describe regional economic inequality. This paper asks whether changes in regional unemployment differences in West Germany are persistent over time. Understanding the persistency of regional unemployment differences helps us to assess how effective regional policy can be. While univariate tests suggest that changes in regional unemployment differences are persistent in West Germany, more powerful panel tests lend some support to the hypothesis that regional unemployment rates converge. However, these tests reveal a moderate speed of convergence at best. Because there is a structural break following the second oil crisis, we also use tests that allow for such a break. This provides evidence for both convergence and quick adjustment to an equilibrium distribution of regional unemployment rates that is, however, subject to a structural break.     

Buyer power and supplier incentives

This paper analyzes the origins and welfare consequences of buyer power. We show that if suppliers are capacity constrained or have strictly convex costs, there are two different channels through which large buyers can obtain more favorable terms from their suppliers. In particular, we show how the presence of large buyers can then erode the value of suppliers’ outside option. Somewhat surprisingly, we show how this can induce suppliers to undertake strategies that lead to higher output and potentially higher welfare.     

Return migration, wage differentials, and the optimal migration duration

In simple static models, migration increases with the wage differential between host- and home-country. In a dynamic framework, and if migrations are temporary, the size of the migrant population in the host country depends also on the migration duration. This paper analyses optimal migration durations in a model which rationalises the decision of the migrant to return to his home country, despite persistently higher wages in the host country. The analysis shows that, if migrations are temporary, the optimal migration duration may decrease if the wage differential grows larger. Using micro data for Germany, the second part of the paper provides empirical evidence which is compatible with this hypothesis.     

Potron and the Perron–Frobenius Theorem

Maurice Potron is an important precursor of the study of linear models of production and, in particular, of input–output analysis. We show that, contrary to Abraham-Frois and Lendjel's interpretation which we consider as unfaithful to Potron's model, there is a clear connection between his theory and the Perron-Frobenius theorem.