Heteroskedasticity and Neglected Parameter Heterogeneity

The paper studies the consequences of neglecting parameter heterogeneity for the linear regression model and cross-sectional data. Monte-Carlo experiments are used to illustrate that neglected parameter heterogeneity typically leads to (a) regression coefficients that are economically meaningless and (b)significant test statistics for heteroskedasticity and, possibly non-normality. The paper concludes that evidence for heteroskedasticity should not routinely lead to the use of White's well-known heteroskedasticity-consistent variance covariance matrix estimator. If heteroskedasticity is caused by neglected parameter heterogeneity or other causes of heteroskedasticity, such as wrong functional form, White's estimator will not serve any useful purpose.     

Social inequalities in travel behaviour: trip distances in the context of residential self-selection and lifestyles

In recent years, the framework of ‘classical’ objective determinants of travel behaviour – such as transport systems, generalised travel costs, life situation and the built environment – has begun to make way for the introduction of subjective elements including attitudes, lifestyles, and location preferences. This paper presents findings from an empirical study of trip distances travelled for three purposes (work, maintenance, leisure). The study was conducted in the region of Cologne, and the analysis is based on structural equation modelling. The results indicate that, in general, neither lifestyles nor location preferences have a strong impact on trip distances, except for leisure activities: here lifestyle has the strongest impact of all variables studied. Maintenance trip distances are significantly affected by the spatial setting in which people live, indicating the relevance of the built environment for this travel segment.     

Extracting cover sets from free fuzzy sorting data

Assignment of items to multiple categories requires suitable statistical methods. The present paper provides a new approach to solve this task. The concept of fuzzy sets is extended to cover sets (sets of overlapping clusters) in a simple manner introducing a vector of item membership sums. The application of the new concept is exemplified by modifying the fuzzy cluster analysis algorithm of Kaufman and Rousseeuw (Finding groups in data: an introduction to cluster analysis, 1990) to cover set cluster analysis appropriately. Wide equivalence of the numerical problems is demonstrated from Lagrange multipliers and Karush-Kuhn-Tucker conditions. Additionally, some extensions are introduced to the algorithm to improve its behavior for suboptimal large or small numbers of clusters. The adapted algorithm in most cases reproduces single sortings for correct numbers of clusters. Two applications to empirical free fuzzy sorting data sets are provided. Limitations of the algorithm are discussed.     

Airport competition - Regional airports losing ground to main airports

Regional airports in Norway are losing market shares to nearby main airports on flights to the national capital, Oslo, and on international travel via Oslo. Travellers are willing to spend several hours extra driving to a larger airport in order to take advantage of lower fares and more convenient airline services. Traffic leakage from regional airports is high when the service from the regional airport is indirect and fare differences are large. Public service obligation tenders (PSO) set maximum fares on the regional legs, but do not cover through travel from regional airports which involve commercial legs. Traffic leakage is particularly evident in the leisure segment. Leakage levels tend to increase as competition is intensified at main airports, but the evidence is rather mixed. Logistic curves of airport market shares have proven to be useful when comparing spatial variations in leakage levels.     

Firm size and job creation in Germany

This paper reports new results on the role of firms from various size classes in the job generation process in Germany. It is based on a unique longitudinal data set covering all manufacturing establishments that existed in at least one year between 1978 and 1993 in the German federal state Lower Saxony. We find that gross job creation and destruction rates tend to decline with firm size, while net job creation rates and firm size are not systematically related when firms are classified according to their average number of employees in the base and end year. Small firms create (destroy) quite a large share of all new (lost) jobs.     

Higher wages in exporting firms: self-selection, export effect, or both? First evidence from linked employer-employee data

While it is a stylized fact that exporting firms pay higher wages than non-exporting firms, the direction of the link between exporting and wages is less clear. Using a rich set of German linked employer-employee panel data we follow over time plants that start to export. We show that the exporter wage premium does already exist in the years before firms start to export, and that it does not increase in the following years. Higher wages in exporting firms are thus due to self-selection of more productive, better paying firms into export markets; they are not caused by export activities.     

Geschäftsprozesskostenrechnung in einem Leasing-Unternehmen

Zur Verbesserung der Wertsch?pfung organisieren sich immer mehr Unternehmen nach Gesch?ftsprozessen. Dies geht h?ufig mit einer Gesch?ftsprozessoptimierung einher, um die Abl?ufe effizient zu gestalten.     

Exports and Productivity Growth: First Evidence from a Continuous Treatment Approach

A recent survey of 54 micro-econometric studies reveals that exporting firms are more productive than non-exporters. However, previous empirical studies show that exporting does not necessarily improve productivity. One possible reason for this result is that most previous studies are restricted to analysing the relationship between a firm’s export status and the growth of its labour productivity, using the firms’ export status as a binary treatment variable and comparing the performance of exporting and non-exporting firms. In this paper, we apply the newly developed generalised propensity score (GPS) methodology that allows for continuous treatment, that is, different levels of the firms’ export activities. Using the GPS method and a large panel data set for German manufacturing firms, we estimate the relationship between a firm’s export-sales ratio and its labour productivity growth rate. We find that there is a causal effect of firms’ export activities on labour productivity growth. However, exporting improves labour productivity growth only within a sub-interval of the range of firms’ export-sales ratios. JEL no.  F14, F23, L60