Periodic integration: further results on model selection and forecasting

This paper considers model selection and forecasting issues in two closely related models for nonstationary periodic autoregressive time series [PAR]. Periodically integrated seasonal time series [PIAR] need a periodic differencing filter to remove the stochastic trend. On the other hand, when the nonperiodic first order differencing filter can be applied, one can have a periodic model with a nonseasonal unit root [PARI]. In this paper, we discuss and evaluate two testing strategies to select between these two models. Furthermore, we compare the relative forecasting performance of each model using Monte Carlo simulations and some U.K. macroeconomic seasonal time series. One result is that forecasting with PARI models while the data generating process is a PIAR process seems to be worse thanvice versa.     

Necessary Edges in k-Chordalisations of Graphs

A k-chordalisation of a graph G = (V,E) is a graph H = (V,F) obtained by adding edges to G, such that H is a chordal graph with maximum clique size at most k. This note considers the problem: given a graph G = (V,E) which pairs of vertices, non-adjacent in G, will be an edge in every k-chordalisation of G. Such a pair is called necessary for treewidth k. An equivalent formulation is: which edges can one add to a graph G such that every tree decomposition of G of width at most k is also a tree decomposition of the resulting graph G. Some sufficient, and some necessary and sufficient conditions are given for pairs of vertices to be necessary for treewidth k. For a fixed k, one can find in linear time for a given graph G the set of all necessary pairs for treewidth k. If k is given as part of the input, then this problem is coNP-hard. A few similar results are given when interval graphs (and hence pathwidth) are used instead of chordal graphs and treewidth.     

Aesthetic leadership

We introduce aesthetic leadership as a promising approach in leadership studies. Two current movements in leadership research, the inclusion of followers in leadership models and the exploration of subjective leadership qualities, make taking an aesthetic perspective in leadership especially attractive and timely. Aesthetics relates to felt meaning generated from sensory perceptions, and involves subjective, tacit knowledge rooted in feeling and emotion. We believe the aesthetics of leadership is an important, but little understood, aspect of organizational life. For example, while we know followers must attribute leadership qualities such as charisma and authenticity to leaders to allow for social influence, we know little about how these processes operate. We propose that followers use their aesthetic senses in making these assessments. We relate aesthetic leadership to several current topics in leadership research, and outline the assumptions and methods of aesthetic leadership.     

Strategic management in a firm of consulting engineers

This article describes the introduction of strategic management in a large and diversified company of consulting engineers in Brazil. This was done by a massive strategic planning effort in which the 60 top people of the company actively participated. This approach was chosen to produce both a comprehensive corporate strategy and strategic management capability throughout the company. The project therefore gave as much attention to training and guidance as to planning itself. Psychological, organizational and ‘political’ factors were taken seriously into account. Project management was a good joint-venture between some top people inside and some external consultants, strongly interacting with each other. The project resulted not only in plans, but also in decisions, including tidying-up the divisional structure of the firm. The article evaluates the project to determine success factors in such undertakings. It is interesting for managers to appreciate the factors involved in efforts to produce plans, develop managers and reorient a company at the same time. It is also interesting because it shows a fruitful, although demanding role for management consultants in strategic reorientations: more committed, more ‘on-line’ than experts submitting recommendations; less amorphous and more performance-oriented than organizational development gurus.     

A New Fully Polynomial Time Approximation Scheme for the Knapsack Problem

A fully polynomial time approximation scheme (FPTAS) is presented for the classical 0-1 knapsack problem. The new approach considerably improves the necessary space requirements. The two best previously known approaches need O(n + 1/³) and O(n · 1/) space, respectively. Our new approximation scheme requires only O(n + 1/²) space while also reducing the running time.     

Temporary vs. permanent migration A decision theoretical approach

The decision problem of the guest worker as a target saver is considered. He plans to accumulate capital in the host country for investment in the home country after return migration. As the worker is supposed to be incompletely informed about the economic variables in the host country he might prolong his stay unexpectedly provided the economic conditions in the host country are unfavourable. Explicit conditions for the economic variables are given such that temporary migration turns into permanent migration.We are indebted to an anonymous referee for helpful comments.     

Simulating Human Behavior for Understanding and Managing Environmental Resource Use

Computer simulation allows for the experimental study of dynamic interactions between human behavior and complex environmental systems. Behavioral determinants and processes as identified in social-scientific theory may be formalized in simulated agents to obtain a better understanding of man–environment interactions and of policy measures aimed at managing these interactions. A number of exemplary agent-based simulation studies is discussed to demonstrate how simulations can be used to identify behavioral determinants and processes underlying environmental problems, and to explore the possible effects of policy strategies. Finally, we highlight how agent-based simulation may contribute to our understanding of the dynamics of environmental resources, and how to manage them in a sustainable way.     

Varieties of commitment

This discussion of some aspects of the problem of conditional normative statements, conditional obligations, or commitments will first focus on some well-known pseudo-paradoxes, then state some different ways of symbolizing conditioned norm statements and, finally, end up with a remark concerning von Wright's interpretation of commitments by means of a logic of necessary and sufficient conditions.     

Risk aversion in n-person bargaining

Relations between risk properties of Pareto optimal n-person bargaining solutions are studied. The (weak) worse alternative property, risk sensitivity property, and risk profit opportunity property are considered, in particular relations between these properties, and between these properties and other properties such as independence of irrelevant alternatives and individual monotonicity. A distinction is made between bargaining games where all Pareto optimal outcomes are riskless, and bargaining games where Pareto optimal outcomes may represent the utilities of lotteries between riskless alternatives. In the first mentioned case, more general results can be obtained.