Familial obesity as a proxy for omitted variables in the obesity-mortality relationship

In a conventional survival analysis of a sample of the U.S. population in 1971-1974, the association between mortality and obesity is compared with the analogous risk from the presence of an obese person in a household. The two factors have similar risk profiles, with a hazard ratio of 1.44 for nonmorbid obesity and 1.48 for nonmorbid familial obesity in one sample. If "familial obesity" cannot directly affect personal longevity, and if shared factors determine both personal and familial obesity, the mortality risk of family and actual personal obesity is similarly overstated. This false positive in the estimated risk arises from correlations among obesity and unobserved environmental, behavioral, or genetic factors.     

Reading “Monosexual”

This essay interrogates the meanings, uses, and implications of the emergent U.S./U.K. bisexual community’s adoption of the term “monosexual” to define non-bisexuals. The authors provide a historical and theoretical context for the term, explicitly linking its oppositional rhetoric to that coined by other recent identity movements, and to that inherent in psychological and psychoanalytical models of identity development. The authors further emphasize their own personal and political responses to and dislike of the term. The essay examines the inconsistencies implicit in the meanings and uses of the term, highlighting the differences between sexual behavior and sexual identity. The unsuitability of the monosexual/bisexual paradigm for a bisexual movement that always overlaps—theoretically, politically, and personally—with other movements is also discussed. The authors conclude by stressing the importance of developing language that expresses the complexity of sexual identity and divergent political affiliation.     

Dynamic Assignment of Flexible Service Resources

Resource flexibility is an important tool for firms to better match capacity with demand so as to increase revenues and improve service levels. However, in service contexts that require dynamically deciding whether to accept incoming jobs and what resource to assign to each accepted job, harnessing the benefits of flexibility requires using effective methods for making these operational decisions. Motivated by the resource deployment decisions facing a professional service firm in the workplace training industry, we address the dynamic job acceptance and resource assignment problem for systems with general resource flexibility structure, i.e., with multiple resource types that can each perform different overlapping subsets of job types. We first show that, for systems containing specialized resources for individual job types and a versatile resource type that can perform all job types, the exact policy uses a threshold rule. With more general flexibility structures, since the associated stochastic dynamic program is intractable, we develop and test three optimization‐based approximate policies. Our extensive computational tests show that one of the methods, which we call the Bottleneck Capacity Reservation policy, is remarkably effective in generating near‐optimal solutions over a wide range of problem scenarios. We also consider a model variant that requires dynamic job acceptance decisions but permits deferring resource assignment decisions until the end of the horizon. For this model, we discuss an adaptation of our approximate policy, establish the effectiveness of this policy, and assess the value of postponing assignment decisions.     

Determinants and consequences of internal control in firms: a contingency theory based analysis

In order to ensure the efficiency and effectiveness of activities, reliability of information and compliance with applicable laws, firms demand adequate internal control. However, several frameworks (COSO, CoCo etc.) assume that the need for internal control varies according to a firm’s characteristics. This concurs with contingency theory, which claims that each organization has to choose the most suitable control system by taking into account contingency characteristics. This study examines which contingency characteristics firms choose to adapt their internal control structure and whether it results in a more favorable assessment of the effectiveness of control by the management. While the components of internal control have been examined individually in the control literature, this paper attempts to shed light on internal control and place it in a broader context. The results, derived from a web-based survey of 741 Finnish firms, indicate that firms adapt their internal control structure to deal with environmental uncertainty and to achieve observed control effectiveness. Also the strategy has statistically significant effects on internal control structure.     

Subhypergraph counts in extremal and random hypergraphs and the fractional <Emphasis Type="Italic">q</Emphasis>-independence

We study the extremal parameter N(n,m,H) which is the largest number of copies of a hypergraph H that can be formed of at most n vertices and m edges. Generalizing previous work of Alon (Isr. J. Math. 38:116–130, 1981), Friedgut and Kahn (Isr. J. Math. 105:251–256, 1998) and Janson, Oleszkiewicz and the third author (Isr. J. Math. 142:61–92, 2004), we obtain an asymptotic formula for N(n,m,H) which is strongly related to the solution α _q (H) of a linear programming problem, called here the fractional q-independence number of H. We observe that α _q (H) is a piecewise linear function of q and determine it explicitly for some ranges of q and some classes of H. As an application, we derive exponential bounds on the upper tail of the distribution of the number of copies of H in a random hypergraph.     

The <Emphasis Type="Italic">p</Emphasis>-maxian problem on block graphs

This paper deals with the p-maxian problem on block graphs with unit edge length. It is shown that the two points with maximum distance provide an optimal solution for the 2-maxian problem of block graphs except for K ₃. It can easily be extended to the p-maxian problem of block graphs. So we solve the p-maxian problem on block graphs in linear time.     

An approximation algorithm for the <Emphasis Type="Italic">k</Emphasis>-level capacitated facility location problem

We consider the k-level capacitated facility location problem (k-CFLP), which is a natural variant of the classical facility location problem and has applications in supply chain management. We obtain the first (combinatorial) approximation algorithm with a performance factor of \(k+2+\sqrt{k^{2}+2k+5}+\varepsilon\) (ε>0) for this problem.     

Strong formulation for the spot 5 daily photograph scheduling problem

Earth observation satellites, such as the SPOT 5, take photographs of the earth according to consumers’ demands. Obtaining a good schedule for the photographs is a combinatorial optimization problem known in the literature as the daily photograph scheduling problem (DPSP). The DPSP consists of selecting a subset of photographs, from a set of candidates, to different cameras, maximizing a profit function and satisfying a large number of constraints. Commercial solvers, with standard integer programming formulations, are not able to solve some DPSP real instances available in the literature. In this paper we present a strengthened formulation for the DPSP, based on valid inequalities arising in node packing and 3-regular independence system polyhedra. This formulation was able, with a commercial solver, to solve to optimality all those instances in a short computation time.