Run length analysis of Shewhart charts applied to drifting processes under an integrative SPC/EPC model

Engineering Process Controllers (EPC) are frequently based on parametrized models. If process conditions change, the parameter estimates used by the controllers may become biased, and the quality characteristics will be affected. To detect such changes it is adequate to use Statistical Process Control (SPC) methods. The run length statistic is commonly used to describe the performance of an SPC chart. This paper develops approximations for the first two moments of the run length distribution of a one-sided Shewhart chart used to detect two types of process changes in a system that is regulated by a given EPC scheme: i) changes in the level parameter; ii) changes in the drift parameter. If the drift parameter shifts, it is further assumed that the form of the drift process changes from a linear trend under white noise (the in-control drift model) into a random walk with drift model. Two different approximations for the run length moments are presented and their accuracy is numerically analyzed. Received: August 1998     

Structural problems of the next few years

The Federal Republic of Germany will be facing in the next few years changes in its economic structure which, if not in their extent, in their effect on the employment situation will be without parallel in the post-war period. After fifteen years of nearly uninterrupted full employment, it is reasonable to expect in the medium term an over-all rate of unemployment of the order of 2–3 p.c. (0.5–0.7 mn).     

Cooperative strategies for the availability service of repairable aircraft components

This paper specifies cooperative strategies for the availability service of repairable aircraft components and finds out which factors contribute to the emergence of a particular cooperative strategy. The strategies ad hoc cooperation, cooperative pooling and commercial pooling were specified and compared to the alternative of acting alone, i.e. solo strategy. A simulation model based on fair assumptions of the cost structure was constructed and the cooperative strategies were tested in a game theoretic setting both from the viewpoint of total efficiency and from the perspective of each participant. Despite the explicit focus on aircraft components, the findings should be relevant to any industry using a closed-loop maintenance process with repairable spare parts.     

Niedrige Preis-Dividende-Verhältnisse: Einstiegssignal für den Aktienmarkt?

Zusammenfassung  Die Finanzmarktkrise ging weltweit mit einem Rückgang der Aktienkurse einher. Sind diese niedrigen Aktien-Bewertungen als überreaktion mit der Aussicht auf baldige Korrektur zu bewerten? Oder bringen sie realistische Erwartungen einer schw?cheren Entwicklung b?rsennotierter deutscher Unternehmen zum Ausdruck? K?nnen anhand der aktuellen Entwicklung der Preis-Dividende-Verh?ltnisse Aussagen über die zukünftige Kurs- und Dividendenentwicklung gemacht werden? Prof. Dr. Oliver Holtem?ller, 37, ist Juniorprofessor für Allgemeine Volkswirtschaftslehre an der Fakult?t für Wirtschaftswissenschaften der Rheinisch-Westf?lischen Technischen Hochschule Aachen.