In this paper, we discuss the shape of the hazard function of Birnbaum-Saunders distribution. Specifically, we establish that the hazard function of Birnbaum-Saunders distribution is an upside down function for all values of the shape parameter. In reliability and survival analysis, as it is often of interest to determine the point at which the hazard function reaches its maximum, we propose different estimators of that point and evaluate their performance using Monte Carlo simulations. Next, we analyze a data set and illustrate all the inferential methods developed here and finally make some concluding remarks.

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In several studies in Survival Analysis, the cause of failure/ death of items or individuals may be attributable to more than one cause. In this chapter, we consider the competing risks model when the data is progressively Type-II censored. We provide different techniques for the analysis of the model under the assumption of independent causes of failure and exponential lifetimes. The maximum likelihood estimators of the different parameters and the UMVUE's are obtained. In addition, the exact distributions of the different estimators are derived. We also derive the UMP and UMPU test for the equality of the failure rates of the competing risks.We consider the Bayesian estimation using the Inverse Gamma distribution as a prior. To assess the performance of all these estimators, confidence intervals are developed using the exact, asymptotic, and bootstrap distributions. In the Bayesian context, we develop credible intervals for the parameters. The different methods are compared through a simulation study, and the analysis of a real dataset. Finally, we also provide some insight into inference under the Weibull model and dependent causes of failure.

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, □atherinq and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information including suggestions for reducing the burden to Department of Defense, Washington Headquarters Services Directorate for Information PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)Wyle Laboratories, Life Sciences, Systems and Services Inc. 2485 Gillingham Drive San Antonio, TX 78235-5105 SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)High SPONSOR/MONITOR'S ACRONYM(S)AFRL/HEPR SPONSOR/MONITOR'S REPORT NUMBER(S) AFRL-HE-BR-TR-2002-0212 DISTRIBUTION/AVAILABILITY STATEMENTApproved for Public Release; distribution is unlimited. SUPPLEMENTARY NOTESThis report will be published in Aviation, Space, and Environmental Medicine as a peer-reviewed article in 2003, Volum 74. ABSTRACTINTRODUCTION. We conducted 25 altitude chamber decompression exposure profiles incorporating both genders in a prospective attempt to clarify the role of gender in DCS susceptibility. METHODS. The 291 human subjects were exposed (961 subject-exposures) to simulated altitude for up to 8 h, using zero to 4 h of preoxygenation. Subjects breathed 100% oxygen, rested or performed mild or strenuous exercise while decompressed, and were monitored for precordial venous gas emboli (VGE) and DCS symptoms. RESULTS. No differences (P=0.24) in DCS incidence were observed between males (49.5%) and females (45.3%). Higher DCS incidence (P < 0.001) was observed in the heaviest males, females with the highest body fat, and in subjects with the highest body mass indices and lowest levels of fitness. CONCLUSION. No differences in altitude DCS incidence were observed between males and females under our test conditions. No apparent need exists for changes in procedures, training, or equipment to enhance protection from DCS based on gender. GENDER NOT A FACTOR FOR ALTITUDE DECOMPRESSION SICKNESS RISK James T. Webb, Nandini Kannan, and Andrew A. Pilmanis ABSTRACT: INTRODUCTION. Early, retrospective reports of the incidence of altitude decompression sickness (DCS) during altitude chamber training exposures indicated that females were more susceptible than males. We hypothesized that a controlled, prospective study would show no significant difference. METHODS. We conducted 25 altitude chamber decompression exposure profiles. A total of 291 human subjects, 197 males and 94 females, underwent 961 exposures to simulated altitude for up to 8 h, using zero to 4 h of preoxygenation. Throughout the exposures, subjects breathed 100% oxygen, rested or performed mild or strenuous exercise, and were monitored for precordial venous gas emboli (VGE) and DCS symptoms. RESULTS. No significant differences in DCS incidence were observed between males (49.5%) and females (45.3%). However, VGE occ...

In this article, we consider a parametric survival model that is appropriate when the population of interest contains long-term survivors or immunes. The model referred to as the cure rate model was introduced by Boag 1 in terms of a mixture model that included a component representing the proportion of immunes and a distribution representing the life times of the susceptible population. We propose a cure rate model based on the generalized exponential distribution that incorporates the effects of risk factors or covariates on the probability of an individual being a long-time survivor. Maximum likelihood estimators of the model parameters are obtained using the the expectation-maximisation (EM) algorithm. A graphical method is also provided for assessing the goodness-of-fit of the model. We present an example to illustrate the fit of this model to data that examines the effects of different risk factors on relapse time for drug addicts.cure rate, long-term survivor, generalized exponential distribution, EM algorithm, goodness-of-fit,

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