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.     

Optimizing the allocation of components to kits in small-lot,multiechelon assembly systems

The kitting problem in multiechelon assembly systems is to allocate on-hand stock and anticipated future deliveries to kits so that cost is minimized. This article structures the kitting problem and describes several preprocessing methods that are effective in refining the formulation. The model is resolved using an optimizing approach based on Lagrangian relaxation, which yields a separable problem that decomposes into a subproblem for each job. The resulting subproblems are resolved using a specialized dynamic programming algorithm, and computational efficiency is enhanced by dominance properties devised for that purpose. The Lagrangian problem is resolved effectively using subgradient optimization and a specialized branching method incorporated in the branch-and-bound procedure. Computational experience demonstrates that the specialized approach outperforms the general-purpose optimizer OSL. The new solution approach facilitates time-managed flow control, prescribing kitting decisions that promote cost-effective performance to schedule. © 1994 John Wiley & Sons. Inc.     

The complementary use of regression diagnostics and robust estimators

Regression modeling for prediction or forecasting purposes is critically dependent on the quality of the data which are used to estimate the model parameters. Extreme response or predictor-variable values can substantially influence least-squares estimates and disproportionately affect predictions. Robust alternatives to least-squares are less sensitive to extreme observations and can provide more precise predictions. In this article diagnostic displays are used to identify extreme observations and to assess the sensitivity of least-squares parameter estimates and predictions to the inclusion of these observations in a data set. The displays are shown to aid in the interpretation of weights which robust estimators assign to influential observations.     

An extremal problem in subconnectivity

The connectivity of a subgraph of a graph can exceed the connectivity of the graph. We call the largest of the connectivities of all subgraphs the subconnectivity. We then give the exact solution to the extremal problem of determining the maximum number of lines in a p-point graph of subconnectivity two.     

Building the Rule of Law: A Model of Police-Military Relations in Latin America

United States policy makers and academic researchers have neglected the deep institutional rivalries between police agencies and military services in Latin America. The problems of police/military coordination have complicated US national goals of democratization, strengthening the rule of law and combating the production and trafficking of illicit drugs in the region. Police agencies stand at the epicenter of dysfunctional criminal justice systems. Although the US policy of engagement with Latin American military services is intended to reorient their roles and missions towards supporting democratically elected civilian governments, US counternarcotics assistance programs have encouraged a wider Latin American military role in drug interdiction. This article develops an analytical model to identify the dimensions of police-military conflict in the context of the fundamental reform of criminal justice systems in Latin America.     

Performance and properties of Q‐Statistic monitoring schemes

In this article, we study the Shewhart chart of Q statistics proposed for the detection of process mean shifts in start‐up processes and short runs. Exact expressions for the run‐length distribution of this chart are derived and evaluated using an efficient computational procedure. The procedure can be considerably faster than using direct simulation. We extend our work to analyze the practice of requiring multiple signals from the chart before responding, a practice sometimes followed with Shewhart charts. The results show that waiting to receive multiple signals severely reduces the probability of quickly detecting shifts in certain cases, and therefore may be considered a risky practice. Operational guidelines for practitioners implementing the chart are discussed. © 2009 Wiley Periodicals, Inc. Naval Research Logistics, 2009     

China's Global Equity Oil Investments: Economic and Geopolitical Influences

In this article, we construct and analyze an original database of overseas Chinese equity oil investments (EOI) in order to assess the relative importance of economic and geopolitical factors in determining the type of countries that are most likely to receive those investments. We find that China's national oil companies (NOCs) choose to make considerable investments in certain oil rich countries while ignoring others. We develop and examine ‘economic opportunity’ and ‘geopolitical relevance’ explanations of Chinese EOI. The economic explanation assumes that Chinese oil companies operate autonomously despite the fact that they are state owned, and that they seek international experience in countries offering less competition but more risk. The geopolitical explanation suggests that Chinese equity oil investments are developed and coordinated by the central government as part of a geopolitical strategy that is designed to bypass the so-called ‘Malacca Dilemma’ and deepen security ties with oil-rich states through the conduct of oil diplomacy. We argue that Chinese EOI tends to reflect both corporate interests and government priorities, and that it generates more liabilities rather than benefits for China.     

Book reviews

John Horsfield, The Art of Leadership in War. The Royal Navy From the Age of Nelson to the End of World War II. Westport, Conn. and London: Greenwood Press, 1980. Pp. 240; £14.75.

John Joseph Timothy Sweet, Iron Arm: The Mechanization of Mussolini's Army, 1920–1940. Westport, Connecticut &; London: Greenwood Press. 1980. Pp. 207; £15.50.

Peter H. Merkl, The Making of a Stormtrooper. Princeton, N.J: Princeton U.P., 1980. Pp. 328; £8.60.

Greg Herken, The Winning Weapon: The Atomic Bomb in the Cold War 1945–1950. New York: Alfred A. Knopf, 1980. Pp. 425; $15.00.

Geoffrey Smith and Nelson W. Polsby, British Government and its Discontents. New York: Basic Books, and London: Harper and Row, 1981. Pp. 202; £7.95.

Seweryn Bialer (ed.), The Domestic Context of Soviet Foreign Policy. Boulder, Colorado: Westview Press and London: Croom Helm, 1981. Pp. 441; £14.95.

Jerry F. Hough, Soviet Leadership in Transition. Washington, D.C.: Brookings Institution and Oxford, Basil Blackwell, 1981. Pp. 175; £12.00 (hb.) and £3.95 (pb.)

Edward F. Mickolus, Transnational Terrorism: A Chronology of Events 1968–1979. London: Aldwych Press, 1980. Pp. 967; £39.95.

Barry Rubin, The Great Powers in the Middle East, 1941–47; The Road to the Cold War, London: Frank Cass, 1980. Pp. 254; £14.50;

Daniel Heradstveit, The Arab‐Israeli Conflict; Psychological Obstacles to Peace. Oslo: Universittsforlaget, 1979. Pp. 234; £11.60;

Janice Gross Stein, and Raymond Tanter, Rational Decision‐making; Israel's Security Choices 1967. Columbus. Ohio; Ohio State University Press, 1980. Pp. 399; $35.     

Bounded flexibility in days‐on and days‐off scheduling

This article presents a flexible days‐on and days‐off scheduling problem and develops an exact branch and price (B&P) algorithm to find solutions. The main objective is to minimize the size of the total workforce required to cover time‐varying demand over a planning horizon that may extend up to 12 weeks. A new aspect of the problem is the general restriction that the number of consecutive days on and the number of consecutive days off must each fall within a predefined range. Moreover, the total assignment of working days in the planning horizon cannot exceed some maximum value. In the B&P framework, the master problem is stated as a set covering‐type problem whose columns are generated iteratively by solving one of three different subproblems. The first is an implicit model, the second is a resource constrained shortest path problem, and the third is a dynamic program. Computational experiments using both real‐word and randomly generated data show that workforce reductions up to 66% are possible with highly flexible days‐on and days‐off patterns. When evaluating the performance of the three subproblems, it was found that each yielded equivalent solutions but the dynamic program proved to be significantly more efficient. © 2013 Wiley Periodicals, Inc. Naval Research Logistics 60: 678–701, 2013