Contrasting the Impacts of Combat and Humanitarian Assistance/Disaster Relief Missions on the Mental Health of Military Service Members

Abstract

We study the differential impacts of combat and humanitarian assistance/disaster relief (HA/DR) missions on the mental health of U.S. Marine Corps members. The deployment experiences of any individual Marine are plausibly random conditional on the observable characteristics which are used to assign Marines into units. Leveraging this exogenous variation, we compare the incidence of post-traumatic stress disorder (PTSD) and suicide deaths among Marines who deployed to either Operation Enduring Freedom/Operation Iraqi Freedom (OEF/OIF) or HA/DR missions between 2001 and 2011. We find that the hazard of PTSD is close to eight times higher among Marines returning from OEF/OIF compared to those never deployed, and just 1.33 times higher among those returning from HA/DR (and never participated in OEF/OIF). Those returning from OEF/OIF missions are 1.81 times more likely than those never deployed to die by suicide when they were still active duty, and the hazard increases to almost 3 after they have left the military. In contrast, we find no difference in the hazards of suicide death between those that deployed to only HA/DR missions and non-deployed Marines.     

Estimating a survival curve when new is better than used with respect to a distinguished set

Hollander, Park, and Proschan define a survival function S of a positive random variable X to be new better than used at age t₀ (NBU-{t₀}) if S satisfies $ \begin{array}{*{20}c} {\frac{{S(x + t_0)}}{{S\left({t_0} \right)}} \le S\left(x \right),} & {{\rm for}\,{\rm all}\,x\, \ge \,0,} \\ \end{array}$ where S(x) = P(X > x). The NBU-{t₀} class is a special case of the NBU-A family of survival distributions, where A is a subset of [0, ∞). These families introduce a variety of modeling possibilities for use in reliability studies. We treat problems of nonparametric estimation of survival functions from these classes by estimators which are themselves members of the classes of interest. For a number of such classes, a recursive estimation technique is shown to produce closed-form estimators which are strongly consistent and converge to the true survival distribution at optimal rates. For other classes, additional assumptions are required to guarantee the consistency of recursive estimators. As an example of the latter case, we demonstrate the consistency of a recursive estimator for S ∈ NBU-[t₀, ∞) based on lifetime data from items surviving a preliminary “burn-in” test. The relative precision of the empirical survival curve and several recursive estimators of S are investigated via simulation; the results provide support for the claim that recursive estimators are superior to the empirical survival curve in restricted nonparametric estimation problems of the type studied here.     

Vector processing approach to constrained network problems

Modification of algorithms designed for scalar computing, to take advantage of vector processing, raises several challenges. This article presents the vectorization of the primal simplex based network algorithm and results in a 50% improvement in computational time. One of the major contributors to this improvement is the matching of the size of the pricing candidate list to the vector register size. The side constraints are relaxed into a single surrogate constraint. The single constraint network algorithm is vectorized and used as the basis for solving large-scale constrained network problems. Computational experiments are presented which illustrate the vectorization of the network code as well as the ability of the surrogate constraint approach to deal with large constrained network problems.     

An infiltration game on k arcs

An infiltrator, starting at a safe base, tries to pass, undetected by a guard and within a time limit, along one of k nonintersecting arcs to a safe destination. Optimal strategies and the value are obtained for this discrete zero-sum search-evasion game.     

When is greedy module assembly optimal?

Many coherent systems are configurations of identically structured modules, each consisting of a number of different components. The objective is to assemble the modules out of a collection of available components, and to install the modules in the system in a way that maximizes reliability. The greedy assembly rule builds one module out of the best available components, another out of the best remaining components, and so on. This article shows that greedy assembly is optimal whenever the modules have a series structure, no matter what the structure of the system in which the modules will be used might be, provided that the modules, once assembled, are installed in the system in an optimal way. The article also demonstrates that series modules are unique in this regard.     

An algorithm and new penalties for concave integer minimization over a polyhedron

We present a branch-and-bound algorithm for globally minimizing a concave function over linear constraints and integer variables. Concave cost functions and integer variables arise in many applications, such as production planning, engineering design, and capacity expansion. To reduce the number of subproblems solved during the branch-and-bound search, we also develop a framework for computing new and existing penalties. Computational testing indicates that penalties based on the Tuy cutting plane provide large decreases in solution time for some problems. A combination of Driebeek-Tomlin and Tuy penalties can provide further decreases in solution time. © 1994 John Wiley & Sons, Inc.     

The survival probability function of a target moving along a straight line in a random field of obscuring elements

A target is moving along a straight-line path. Random portions of the path might be invisible to the hunter (in shadow). Shooting trials are conducted only along the visible segments of the path. An algorithm for the numerical determination of the survival probability of the target is developed. This algorithm is based on the distribution of shadow length, which is also developed. © 1994 John Wiley & Sons, Inc.     

Stochastic comparisons for single-server queues

We consider single-server queueing systems with the queue discipline “first come, first served,” interarrival times {u_k, k ≥ l}, and service times {u_k, k ≥ l}, where the {u_k} and {u_k} are independent sequences of non-negative random variables that are independently but not necessarily identically distributed. Let X_k = u_k − u_k (k ≥ 1), S₀ 0, S_n = X₁ + X₂ … + X_n(n≥1). It is known that the (possibly nonhomogeneous) random walk {S_n} determines the behavior of the system. In this paper we make stochastic comparisons of two such systems σ₁,σ₂ whose basic random variables X and X are stochastically ordered. The corresponding random walks are also similarly ordered, and this leads to stochastic comparisons of idle times, duration of busy period and busy cycles, number of customers served during a busy period, and output from the system. In the classical case of identical distributions of {u_k} and {u_k} we obtain further comparisons. Our results are for the transient behavior of the systems, not merely for steady state.     

Reliability control for mission-critical items

Reliability control for mission-critical items is studied. The purpose of the control is to ensure the attainment during mission time of a required performance level which is based on suitably defined measures. This is achieved by replacing the item during normal operation time as soon as the reliability requirement is violated. We first consider the case of a known life distribution, but the main focus of the work is on the case where the life distribution is not completely specified. A Bayesian approach is taken and a replacement procedure is constructed on the basis of the overall uncertainty we face, namely, the stochastic failure process and our (continuously revised) probabilistic assessment of the underlying life distribution. The resulting replacement policy is investigated and detailed results are obtained for some common life distributions.