Implementation of college admission rules

Summary We consider both Nash and strong Nash implementation of various matching rules for college admissions problems. We show that all such rules are supersolutions of the stable rule. Among these rules the lower bound stable rule is implementable in both senses. The upper bound Pareto and individually rational rule is strong Nash implementable yet it is not Nash implementable. Two corollaries of interest are the stable rule is the minimal (Nash or strong Nash) implementable solution that is Pareto optimal and individually rational, and the stable rule is the minimal (Nash or strong Nash) implementable extension of any of its subsolutions.We wish to thank Professor William Thomson for his efforts in supervision as well as his useful suggestions. We are grateful to the participants in his reading class, workshops at Bilkent University, University of Rochester, and in particular Jeffrey Banks, Stephen Ching, Bhaskar Dutta, Rangarajan Sundaram and an anonymous referee for their helpful comments.     

Learning competitive market balance

Summary We exhibit a quite natural, adaptive process generated by price-taking, noncooperative firms, supplying the same market. Under rather mild conditions, that process, being driven by marginal profits, converges to a market clearing, Cournot-Nash equilibrium. Namely, it suffices for convergence that cost functions be strictly convex and that the law of demand holds. Randomness in revenues and costs is accommodated.Support from Ruhrgas is gratefully acknowledged.     

Politically stable pay-as-you-go pension systems: When the social-insurance budget is too small in a democracy

The essay analyzes in an overlapping-generations model, to which extent a pay-as-you-go pension system will be the outcome of majority voting, given specific institutional set-ups. Clearly, the vote of an active person depends on his expectations about how the present decision (i.e., his contribution) is linked to the future (i.e., his benefits), when he will be retired. In the paper we employ the assumption of a basic social contract where each active voter's future benefits are positively related to his contributions. It is shown that in this framework a steady-state with a positive (though lower than optimal) level of the pension system exists, even if a new majority decision about the system takes place every period.     

On the fundamental thought behind voting rules

The theme is Arrow's requirement in his theorem of 1951 on methods for group choice, that the choice be independent of irrelevant alternatives. The attention is drawn to (1) his own explanation of this requirement in 1972, which is a quite different understanding than has been discussed in the voluminous literature on the theorem, (2) that Arrow, in fact, in 1985 showed an understanding for how irrelevant alternatives might in a meaningful way influence the group choice, (3) that admittedly the border-line between irrelevant and relevant alternatives in Arrow's original statement is arbitrary, and (4) that Arrow, if he had observed the final thought in the origin of the group theory by Borda, which he admittedly did not, might have realized that Borda's method stringently estimates the relevance of each alternative for the result.The author expresses his surprise that a theoretical conclusion based on an arbitrary fundament has been admired so long.     

German rail vehicle construction in the context of market globalisation

Conclusion In the guise of ABB Daimler-Benz Transportation and Siemens, Germany has two powerful systems suppliers in a good position to keep pace with other systems suppliers on global markets. As in the air-travel industry it is conceivable that developments are moving towards a uniform rail technology. Although the buy national principle still dominates procurement practices, and national egos still dominate the development of rail systems (ICE, TGV), growing competition from Japan could force Europe to develop a European system. This would significantly increase the chances of European industry in bidding for international contracts. For this reason the EU should not relent in its efforts to standardise European rail systems.     

How Often to Sample a Continuous-Time Process in the Presence of Market Microstructure Noise

In theory, the sum of squares of log returns sampled at highfrequency estimates their variance. When market microstructurenoise is present but unaccounted for, however, we show thatthe optimal sampling frequency is finite and derives its closed-formexpression. But even with optimal sampling, using say 5-minreturns when transactions are recorded every second, a vastamount of data is discarded, in contradiction to basic statisticalprinciples. We demonstrate that modeling the noise and usingall the data is a better solution, even if one misspecifiesthe noise distribution. So the answer is: sample as often aspossible.     

Erklärungsansätze für vertragswidriges Verhalten Versicherungsnehmern aus Sicht der ökonomischen Theorie

The two main purposes of this paper are an introduction to the economic analysis of insurance fraud and furthermore a derivation of factors that determine fraudulent behavior of policyholders on insurance markets. Consequently, we analyze the strategic decision problems of insurance companies and the policyholders and identify some factors that can help to reduce fraudulent behavior. In this context we evaluate two derived starting points for the combat against insurance fraud: fraud detection systems and a consequent charge policy of detected defrauders. We illustrate that both points can help to reduce the cost of fraud. Furthermore, we enhance our earlier analysis with respect to the empirical fact that some individuals care about fairness or — in the insurance fraud context — the legitimacy of their actions. Surprisingly, in some market situations these concerns of some policyholders do not lead to a lower fraud probability. Finally, we discuss how and to what extent insurance companies can influence such ethical concerns of policyholders. On that score, we distinguish insurance specific and insurance unspecific factors and their impact on the consumers attitudes towards insurance fraud.     

Langlebigkeit und Altern: Gene oder Umwelt?

Aging is defined as loss of homeostasis which affects all metabolic systems, including DNA. Interspecies comparisons and lessons from the human genetic instability syndromes suggest a correlation between DNA-homeostasis and maximum lifespan, whereas average lifespan depends mainly on environmental factors. Current demographic data suggest a maximum lifespan in humans of 110–115. The average life expectancy at birth has reached 80 years in the wealthy nations and may exceed, at least in females, 90 years by the year 2050. Genetic and biological reasons, but also lifestyle factors, account for the greater longevity of women. Attempt to define a ?longevity“ genotype so far have not been met with success, but carriers of the ApoE4-Allele appear to have a disadvantage. Unlike the situation in model organisms, aging and longevity in humans seem to be influenced by numerous genes and environmental interactions. Most people do not die of old age but of age-related diseases which are frequent because of lack of natural selection against genetic defects that cause late-onset diseases. Moreover, genes causing late-onset diseases show evidence of antagonistic pleiotropy, rendering these genes resistant to removal from our genome. Likewise, thermoinstability of DNA and generation of reactive oxygen species during oxidative phosphorylation are two endogenous sources of genomic instability that limit our lifespan and cannot be overcome without fundamentally altering the biological make-up of our species. Genomic instability causes cancer and accelerates the aging process, as evidenced by the human caretaker gene syndromes which typically show progeroid features. From a genetic point of view, cancer and aging may be moderately delayed and / or mitigated by lifestyle and medical / environmental interventions, but given the constraints of our biological make-up, they cannot be eradicated.