Annual arrival cycle of Atlantic tropical cyclones

Tropical cyclones occur in the North Atlantic Ocean and the Gulf of Mexico throughout the year. This paper statistically quantifies their annual arrival cycle. A Poisson process with a periodic time-varying intensity function is used to model the annual cycle of storm arrivals. The kernel method is used to estimate the time-varying intensity function. A data set that contains storm occurrence dates for the 120-year period 1871-1990 inclusive is analyzed. The estimated intensity function indicates that the peak of the hurricane season is around 12 September and that the true intensity function may be multi-modal. Adjustments are made in the analysis to account for storms that occurred but went unrecorded over the earlier years of the data record.     

The Population Mean and the Proportion of Frequent Gamblers: Is the Theory of Total Consumption Valid for Gambling?

The study looks at three representative samples of Norwegians in different age groups with the aim of finding evidence for the validity of the total consumption model for the area of gambling. The results show that gambling was distributed in the population in a way consistent with the predictions of the total consumption theory. Populations with a low mean gambling frequency had a lower proportion of frequent gamblers than populations with a high mean gambling frequency. It was also shown that in a population with a low mean gambling frequency, consumers along the whole consumption continuum gambled less frequently, than in a population with a high mean gambling frequency. It is concluded that the total consumption model seems to be valid for gambling, and that gambling consequently needs to be understood as a public health issue. The actions and behaviours of the normal majority can then not be regarded as irrelevant for the development in problem gambling prevalences.     

Beratung virtueller Teams im interkulturellen Kontext – ein Bericht aus der Praxis

Tasks are nowadays increasingly assigned to teams composed of members from different cultures who have to work together regardless of country borders or time zones. This causes special challenges for all parties involved in such work settings. Consultancy has accordingly to face the resulting increase of complexity: within the scope of an intercultural consulting process it becomes vital to take into consideration the often postulated focus on both differences and commonalities as well as to consider the dynamics within team processes. This article tries to reflect our work with “virtual teams” which consist of members having different cultures. We try to combine popular intercultural models with a systemic-constructivistic approach as well as with knowledge about group dynamics in order to make sure that a productive outcome is possible in a consulting process. In doing so we work on three levels: individual reflection with the participants’ own culture which is then combined with those of the other team members and then finally the group’s specific team culture is addressed and discussed. At the end of the article we summarize implications for consulting and management when working with virtual teams in an intercultural setting.     

Gambling Behaviour and the Prevalence of Gambling Problems in Adult EGM Gamblers when EGMs are Banned. A Natural Experiment

In this article, findings of a panel study among former EGM gamblers are discussed. The data were collected in two waves during 2007, and 1293 people, 18 years or older, participated. The background for the study was the Norwegian ban on EGMs from 1 July 2007, and the aim was to investigate how this ban affected gambling involvement and problem levels in the sample. The analysis shows that gambling participation, gambling frequencies and gambling problems were reduced after EGMs disappeared from the market. There was no indication of the development of an illegal EGM market, or of substitution of EGMs with other types of gambling. A reduction in other types of gambling is interpreted as an indication of synergetic effects between games. Reduced gambling participation among the most active EGM gamblers, and among risk gamblers, shows that the reductions in gambling availability had an effect even on highly involved gamblers.     

The asymmetric environmental consequences of population change: an exploratory county-level study of land development in the USA, 2001-2011

In this exploratory study, we decompose population growth and decline into their constituent elements to examine how demographic change drives environmental change. Using the example of land development, the analysis integrates county-level measures of births, deaths, in-migration, and out-migration with data on built-up land area from the National Land Cover Database for the years 2001–2006 and then 2006–2011. Drawing from human ecology and environmental demography, we hypothesize that the components of population change will have asymmetric impacts on the construction of the built environment as a form of land development. Results from spatial error models, with a contemporaneous and a temporarily lagged dependent variable, show conditional support for these hypotheses. While each component of demographic change has a unique effect on the dependent variable, the rate at which births increase built-up land area is significantly greater than the rate at which deaths slow this process down.     

Befriending the same differently: ethnic,socioeconomic status,and gender differences in same-ethnic friendship

This study examines same-ethnic friendship variation between students from different ethnic, socioeconomic, and gender groups. Hypotheses based on a theoretical framework of opportunities, preferences, and third-party influence are tested on data of 11,063 students in English, German, Dutch, and Swedish school classes. Using structural equation modelling, the results indicate that ethnic groups differ in absolute and relative same-ethnic friendship because of different meeting opportunities with same-ethnic peers in class and a different status in the ethnic hierarchy. Socioeconomic status groups differ in same-ethnic friendship because socioeconomic status sorts students into more or less diverse school classes but not consistently so across countries and groups. Little further evidence is found for a relation between socioeconomic status and same-ethnic friendship preferences. Lastly, boys and girls do not seem to differ much regarding same-ethnic friendship.     

Kosten und Kostentreiber von unerwünschten Werbemails (Spam) — Eine empirische Analyse auf Provider- und Anwenderseite

Zusammenfassung  In der Literatur wird diskutiert, dass unerwünschte Werbemails (Spam) sowohl auf individueller als auch auf volkswirtschaftlicher Ebene erhebliche Kosten verursachen, deren H?he jedoch unbestimmt ist. Diese Fragestellung wird mit zwei empirischen Untersuchungen adressiert, in denen die Mitarbeiter einer Universit?t zu ihren Spam-Kosten befragt wurden. Die Daten werden mit Hilfe von Finite Mixture Regressions analysiert. In der Betrachtung der Kosten ergibt sich der Befund, dass die auf individueller Ebene entstehenden Kosten die zentralen Kosten auf IT-Ebene deutlich übersteigen. Es zeigt sich, dass die Spam-Belastung bei den Mitarbeitern heterogen verteilt ist und dass ein Spamfilter vor allem bei stark belasteten Nutzern zu einer Kostenersparnis führt. Um die Heterogenit?t in der Spam-Wahrnehmung und die Angst vor Fehlklassifikationen zu berücksichtigen, sollten die Nutzer die M?glichkeit haben, auf einfache Art auf den Filterprozess einzuwirken.

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Costs and cost drivers of unsolicited bulk email (spam) — an empirical analysis

Summary  This paper empirically addresses the often claimed assumption that unsolicited bulk e-mail (spam) causes significant costs — on the individual level as well as for the entire society. To shed light on this problem, employees of a large university were interviewed twice in order to determine the individual costs caused by spam and to identify the relevant cost drivers using finite mixture regressions. The results indicate a heterogeneous distribution of spam load and the resulting costs. The panel approach yields the conclusion that spam filters lead to a reduction of costs only for users severely troubled by spam. Furthermore, people tend to become active against spam only when a certain threshold of spam burden is reached. The costs caused by spam for the users exceed the central IT-related expenses by far. For the implementation of spam filters the results suggest a two step procedure to be most efficient: central actions should be taken to block e-mails that can be unambiguously identified as spam. Further, users should be given the opportunity to influence the filtering process in order to account for heterogeneity and their fear of false classification.

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Die Autoren bedanken sich sehr herzlich bei den Mitarbeitern des Rechenzentrums der Christian-Albrechts-Universit?t zu Kiel für die intensive Kooperation. Wir danken zudem Prof. Dr. Dr. h.c. S?nke Albers, Christian Barrot, Eva Bl?meke und Christina Schmidt-St?lting für die zahlreichen Hinweise zu früheren Fassungen des Aufsatzes. Auch die beiden Gutachter und das Herausgeberteam der ZfB haben zahlreiche Verbesserungsvorschl?ge gemacht, die zu einer substanziellen Verbesserung des Manuskripts geführt haben.     

A network epidemic model for online community commissioning data

A statistical model assuming a preferential attachment network, which is generated by adding nodes sequentially according to a few simple rules, usually describes real-life networks better than a model assuming, for example, a Bernoulli random graph, in which any two nodes have the same probability of being connected, does. Therefore, to study the propagation of “infection” across a social network, we propose a network epidemic model by combining a stochastic epidemic model and a preferential attachment model. A simulation study based on the subsequent Markov Chain Monte Carlo algorithm reveals an identifiability issue with the model parameters. Finally, the network epidemic model is applied to a set of online commissioning data.