The Detection of Nuclear Materials Losses*

The identification and location of materials losses in nuclear facilities is an important issue. Many complexities arise in monitoring such losses. These complexities include the dependency among materials balance observations and the influence of errors (outliers) on parameter estimates of various monitoring methods. The proposed Joint Estimation procedure is superior to standard methods (control chart and CUSUM) and to methods that build in correlation (ARMA control chart, ARMA CUSUM, and the Generalized M procedure) in the detection of nuclear materials losses. The Joint Estimation procedure is robust to the influence of outliers, is flexible in accommodating a range of dependencies among observations, and provides information on the type of loss. Further, the procedure is reliable in that it yields a probability of false alarms and a probability of detecting losses closer to specifications.     

OPTIMAL PORTFOLIO SELECTION OF BONDS AND STOCKS*

In the present study, we offer an alternative approach to bond portfolio management which differs from the traditional immunization approach. In doing so, we formalize what has been a common practice among some investors who form portfolios of bonds and stocks with a view to optimizing the trade-off between risk and return. By using the general multiindex model to characterize the variance-covariance structure of security returns, both duration theory and modern equilibrium theories of the term structure are incorporated in the analysis. In addition, a simplified selection procedure based on a single-index model is derived. This procedure is intuitively appealing to practitioners since it selects assets on the basis of reward per unit of risk of individual assets.     

EFFECTS OF BUDGETARY CONTROL DESIGN ON MANAGEMENT DECISIONS: SOME EMPIRICAL EVIDENCE*

An examination of budgetary slack behavior reveals that managerial characteristics and the economic environment may contribute to the failure of budgetary control systems. Large management-controlled firms that operate in industries with high barriers to entry behave as if they allocate more slack resources when compared with owner-controlled firms of similar size and market power. The results confirm that accounting operating-income numbers reflect manifestations of slack behavior in the budgetary process. Management-controlled firms in particular seem to act as if they fail to release and redistribute slack resources. It is concluded that budgetary slack behavior points to failures in the organization design that may lead to inefficient allocation of resources and to inferior profit performance.     

Risk filtering, ranking, and management framework using hierarchical holographic modeling.

This paper contributes a methodological framework to identify, prioritize, assess, and manage risk scenarios of a large-scale system. Qualitative screening of scenarios and classes of scenarios is appropriate initially, while quantitative assessments may be applied once the set of all scenarios (hundreds) has been prioritized in several phases. The eight-phase methodology is described in detail and is applied to operations other than war. The eight phases are as follows: Phase I, Scenario Identification-A hierarchical holographic model (HHM) is developed to describe the system's "as planned" or "success" scenario. Phase II, Scenario Filtering-The risk scenarios identified in Phase I are filtered according to the responsibilities and interests of the current system user. Phase III, Bi-Criteria Filtering and Ranking. Phase IV, Multi-Criteria Evaluation. Phase V, Quantitative Ranking-We continue to filter and rank scenarios based on quantitative and qualitative matrix scales of likelihood and consequence; and ordinal response to system resiliency, robustness, redundancy. Phase VI, Risk Management is performed, involving identification of management options for dealing with the filtered scenarios, and estimating the cost, performance benefits, and risk reduction of each. Phase VII, Safeguarding Against Missing Critical Items--We examine the performance of the options selected in Phase VI against the scenarios previously filtered out during Phases II to V. Phase VIII, Operational Feedback-We use the experience and information gained during application to refine the scenario filtering and decision processes in earlier phases. These eight phases reflect a philosophical approach rather than a mechanical methodology. In this philosophy, the filtering and ranking of discrete scenarios is viewed as a precursor to, rather than a substitute for, consideration of the totality of all risk scenarios.     

Families of splitting criteria for classification trees

Several splitting criteria for binary classification trees are shown to be written as weighted sums of two values of divergence measures. This weighted sum approach is then used to form two families of splitting criteria. One of them contains the chi-squared and entropy criterion, the other contains the mean posterior improvement criterion. Both family members are shown to have the property of exclusive preference. Furthermore, the optimal splits based on the proposed families are studied. We find that the best splits depend on the parameters in the families. The results reveal interesting differences among various criteria. Examples are given to demonstrate the usefulness of both families.     

On the use of surrogate end points in randomized trials

In a recent paper Day and Duffy proposed a strategy for designing a randomized trial of different breast cancer screening schedules. Their strategy was based on the use of predictors of mortality determined by patients' factors at diagnosis as surrogates for true mortality. On the basis of the Prentice criterion for validity of a surrogate end point, and data from earlier studies of breast cancer case survival, they showed that, not only would the trial require a much shorter follow-up, but also that the information (i.e. inverse variance) for evaluating a treatment effect on mortality would be greater by a factor of nearly 3 if the predictors of mortality were used, compared with a trial in which mortality was actually observed. Although these results are technically correct, we believe that the conceptual strategy on which they are based is flawed, and that the fundamental problem is the Prentice criterion itself. In this paper the technical issues are discussed in detail, and an alternative structure for evaluating the validity of surrogate end points is proposed.     

Nonlinear Regressions with Integrated Time Series

An asymptotic theory is developed for nonlinear regression with integrated processes. The models allow for nonlinear effects from unit root time series and therefore deal with the case of parametric nonlinear cointegration. The theory covers integrable and asymptotically homogeneous functions. Sufficient conditions for weak consistency are given and a limit distribution theory is provided. The rates of convergence depend on the properties of the nonlinear regression function, and are shown to be as slow as n^1/4 for integrable functions, and to be generally polynomial in n^1/2 for homogeneous functions. For regressions with integrable functions, the limiting distribution theory is mixed normal with mixing variates that depend on the sojourn time of the limiting Brownian motion of the integrated process.     

Reliability,Validity, and Cut Scores of the South Oaks Gambling Screen (SOGS) for Chinese

We examined the reliability, validity, and classification accuracy of the South Oaks Gambling Screen (SOGS) when adopted for use in Chinese. The DSM-IV criteria for pathological gambling served as the standard against which the classification accuracy of the SOGS was tested. A total of 283 Chinese adults in the community and 94 Chinese treatment-seeking gamblers were recruited. The internal reliability of the SOGS was satisfactory for the general sample and acceptable for the gambling sample. The SOGS was correlated with the DSM-IV criteria items as well as psychosocial and gambling-related problems. Relative to the DSM-IV criteria, the SOGS tended to overestimate the number of pathological gamblers in both samples. In general, we were relatively confident that individuals were not pathological gamblers if the SOGS scores were between 0 and 4 and were pathological gamblers if the SOGS were between 11 and 20. There was about 50–50 chance of being pathological gamblers if the SOGS scores were between 8 and 10. However, the probability of individuals being pathological gamblers was about 0.30 if the SOGS scores were between 5 and 7. We proposed a SOGS cut score of 8 to screen for probable pathological gambling in Chinese societies.