Maurice C. Bryson

Bio: Maurice C. Bryson is an academic researcher from Los Alamos National Laboratory. The author has contributed to research in topics: Covariate & Regression analysis. The author has an hindex of 6, co-authored 9 publications receiving 1028 citations.

Statistical Analysis of Reliability and Life-Testing Models

Abstract: (1992). Statistical Analysis of Reliability and Life-Testing Models. Technometrics: Vol. 34, No. 4, pp. 486-487.

Some Criteria for Aging

Abstract: The concept of “aging,” or progressive shortening of an entity's residual lifetime, is discussed in terms of the entity's survival time distribution. Quantities defined to describe the aging phenomenon include the “specific aging factor,” “hazard rate,” “hazard rate average,” and “mean residual lifetime.” A set of seven criteria for aging is established, based on these quantities, and a chain of implications among the criteria is developed. The hazard rate average and mean residual lifetime are noted as being particularly useful for empirical studies. An application of these two quantities is illustrated for a set of empirical survival time data.

Probability Statistics, and Reliability for Engineers

Abstract: Introduction: Introduction. - Types of Uncertainty. - Taylor Series Expansion. - Applications. - Problems. - Data Description and Treatment: Introduction.- Classification of Data. - Graphical Description of Data. - Histograms and Frequency Diagrams. - Descriptive Measures. - Applications. - Problems. - Fundamentals Of Probability: Introduction. - Sample Spaces, Sets, and Events. - Mathematics of Probability. - Random Variables and Their Probability Distributions. - Moment.- Common Discrete Probability Distributions. - Common Continuous Probability Distributions. - Applications. - Problems. - Multiple Random Variables: Introduction. - Joint Random Variables and Their Probability Distributions. - Functions of Random Variables. - Applications. - Problems. - Fundamentals of Statistical Analysis: Introduction. - Estimation of Parameters. - Sampling Distributions. - Hypothesis Testing: Procedure. - Hypothesis Tests of Means. - Hypothesis Tests of Variances. - Confidence Intervals. - Sample-Size Determination. - Selection of Model Probability Distributions. - Applications. Problems. - Curve Fitting and Regression Analysis: Introduction. - Correlation Analysis. - Introduction to Regression. - Principle of Least Squares. - Reliability of the Regression Equation. - Reliability of Point Estimates of the Regression Coefficients. - Confidence Intervals of the Regression Equation. - Correlation Versus Regression. - Applications of Bivariate Regression Analysis. - Multiple Regression Analysis. - Regression Analysis of Nonlinear Models. - Applications. Problems. - Simulation: Introduction. - Monte Carlo Simulation. - Random Numbers. - Generation of Random Variables. - Generation of Selected Discrete Random Variables. - Generation of Selected Continuous Random Variables. - Applications. - Problems. - Reliability and Risk Analysis: Introduction. - Time to Failure. - Reliability of Components. - Reliability of Systems. - Risk-Based Decision Analysis. - Applications. - Problems. - Bayesian Methods: Introduction. - Bayesian Probabilities. - Bayesian Estimation of Parameters. - Bayesian Statistics. - Applications. - Problems. - Appendix A: Probability and Statistics Tables. - Appendix B: Values of the Gamma Function. - Subject Index.

The Incidence of Monotone Likelihood in the Cox Model

Abstract: In estimating covariate coefficients for the Cox proportional-hazards model, there is a nonzero probability for any finite sample that the maximum likelihood estimate will be infinite. This implies that in Monte Carlo studies the variance is not a suitable estimator of precision. This also may necessitate a stratified analysis when multiple covariates are involved. A simple method is given for detecting and handling these infinite estimates.

Covariate analysis of survival data: a small-sample study of Cox's model

Abstract: Cox's proportional-hazards model is frequently used to adjust for covariate effects in survival-data analysis. The small-sample performances of the maximum partial likelihood estimators of the regression parameters in a two-covariate hazard function model are evaluated with respect to bias, variance, and power in hypothesis tests. Previous Monte Carlo work on the two-sample problem is reviewed.

A solution to the problem of separation in logistic regression

Abstract: The phenomenon of separation or monotone likelihood is observed in the fitting process of a logistic model if the likelihood converges while at least one parameter estimate diverges to +/- infinity. Separation primarily occurs in small samples with several unbalanced and highly predictive risk factors. A procedure by Firth originally developed to reduce the bias of maximum likelihood estimates is shown to provide an ideal solution to separation. It produces finite parameter estimates by means of penalized maximum likelihood estimation. Corresponding Wald tests and confidence intervals are available but it is shown that penalized likelihood ratio tests and profile penalized likelihood confidence intervals are often preferable. The clear advantage of the procedure over previous options of analysis is impressively demonstrated by the statistical analysis of two cancer studies.

Generalized Exponential Distributions

Abstract: Summary The three-parameter gamma and three-parameter Weibull distributions are commonly used for analysing any lifetime data or skewed data. Both distributions have several desirable properties, and nice physical interpretations. Because of the scale and shape parameters, both have quite a bit of flexibility for analysing different types of lifetime data. They have increasing as well as decreasing hazard rate depending on the shape parameter. Unfortunately both distributions also have certain drawbacks. This paper considers a three-parameter distribution which is a particular case of the exponentiated Weibull distribution originally proposed by Mudholkar, Srivastava & Freimer (1995) when the location parameter is not present. The study examines different properties of this model and observes that this family has some interesting features which are quite similar to those of the gamma family and the Weibull family, and certain distinct properties also. It appears this model can be used as an alternative to the gamma model or the Weibull model in many situations. One dataset is provided where the three-parameter generalized exponential distribution fits better than the three-parameter Weibull distribution or the three-parameter gamma distribution.

A new study on reliability-based design optimization

Abstract: This paper presents a general approach for probabilistic constraint evaluation in the reliability-based design optimization (RBDO). Different perspectives of the general approach are consistent in prescribing the probabilistic constraint, where the conventional reliability index approach (RIA) and the proposed performance measure approach (PMA) are identified as two special cases. PMA is shown to be inherently robust and more efficient in evaluating inactive probabilistic constraints, while RIA is more efficient for violated probabilistic constraints. Moreover, RBDO often yields a higher rate of convergence by using PMA, while RIA yields,singularity in some cases.

Exponentiated exponential family: an alternative to gamma and weibull distributions

Abstract: Summary In this article we study some properties of a new family of distributions, namely Exponentiated Exponentialdistribution, discussed in Gupta, Gupta, and Gupta (1998). The Exponentiated Exponential family has two parameters (scale and shape) similar to a Weibull or a gamma family. It is observed that many properties of this new family are quite similar to those of a Weibull or a gamma family, therefore this distribution can be used as a possible alternative to a Weibull or a gamma distribution. We present two reall ife data sets, where it is observed that in one data set exponentiated exponential distribution has a better fit compared to Weibull or gamma distribution and in the other data set Weibull has a better fit than exponentiated exponential or gamma distribution. Some numerical experiments are performed to see how the maximum likelihood estimators and their asymptotic results work for finite sample sizes.

Hybrid Analysis Method for Reliability-Based Design Optimization

Abstract: Reliability-Based Design Optimization (RBDO) involves evaluation of probabilistic constraints, which can be done in two different ways, the Reliability Index Approach (RIA) and the Performance Measure Approach (PMA). It has been reported in the literature that RIA yields instability for some problems but PMA is robust and efficient in identifying a probabilistic failure mode in the RBDO process. However, several examples of numerical tests of PMA have also shown instability and inefficiency in the RBDO process if the Advanced Mean Value (AMV) method, which is a numerical tool for probabilistic constraint evaluation in PMA, is used, since it behaves poorly for a concave performance function, even though it is effective for a convex performance function. To overcome difficulties of the AMV method, the Conjugate Mean Value (CMV) method is proposed in this paper for the concave performance function in PMA. However, since the CMV method exhibits the slow rate of convergence for the convex function, it is selectively used for concave-type constraints. That is, once the type of the performance function is identified, either the AMV method or the CMV method can be adaptively used for PMA during the RBDO iteration to evaluate probabilistic constraints effectively. This is referred to as the Hybrid Mean Value (HMV) method. The enhanced PMA with the HMV method is compared to RIA for effective evaluation of probabilistic constraints in the RBDO process. It is shown that PMA with a spherical equality constraint is easier to solve than RIA with a complicated equality constraint in estimating the probabilistic constraint in the RBDO process. NOMENCLATURE X