Nuclear Plant Systems Analysis Research at EPRI

A synopsis is given of research projects on probabilistic systems analysis conducted by the Risk Assessment Program of the Electric Power Research Institute. A brief outline of the value of systems analysis both within PRA and as a stand-alone discipline is used to show how the objectives of the research program are related to industry needs. Research projects and their deliverables are discussed in relation to three objectives: (1) to improve the credibility of the methods and results, (2) to provide computer tools and technology transfer, and (3) to develop use of the methods to improve safety and availability in operation. Recent achievements and future plans are briefly described and an up to date list of relevant EPRI publications is provided.     

Historical controls and modern survival analysis

Comparison of observed mortality with known, background, or standard rates has taken place for several hundred years. With the developments of regression models for survival data, an increasing interest has arisen in individualizing the standardisation using covariates of each individual. Also, account sometimes needs to be taken of random variation in the standard group.Emphasizing uses of the Cox regression model, this paper surveys a number of critical choices and pitfalls in this area. The methods are illustrated by comparing survival of liver patients after transplantation with survival after conservative treatment.     

Infant Smiling Dynamics and Perceived Positive Emotion

To better understand early positive emotional expression, automated software measurements of facial action were supplemented with anatomically based manual coding. These convergent measurements were used to describe the dynamics of infant smiling and predict perceived positive emotional intensity. Over the course of infant smiles, degree of smile strength varied with degree of eye constriction (cheek raising, the Duchenne marker), which varied with degree of mouth opening. In a series of three rating studies, automated measurements of smile strength and mouth opening predicted naïve (undergraduate) observers’ continuous ratings of video clips of smile sequences, as well as naïve and experienced (parent) ratings of positive emotion in still images from the sequences. An a priori measure of smile intensity combining anatomically based manual coding of both smile strength and mouth opening predicted positive emotion ratings of the still images. The findings indicate the potential of automated and fine-grained manual measurements of facial actions to describe the course of emotional expressions over time and to predict perceptions of emotional intensity.     

Statistical profiling methods with hierarchical logistic regression for healthcare providers with binary outcomes

Within the context of California's public report of coronary artery bypass graft (CABG) surgery outcomes, we first thoroughly review popular statistical methods for profiling healthcare providers. Extensive simulation studies are then conducted to compare profiling schemes based on hierarchical logistic regression (LR) modeling under various conditions. Both Bayesian and frequentist's methods are evaluated in classifying hospitals into ‘better’, ‘normal’ or ‘worse’ service providers. The simulation results suggest that no single method would dominate others on all accounts. Traditional schemes based on LR tend to identify too many false outliers, while those based on hierarchical modeling are relatively conservative. The issue of over shrinkage in hierarchical modeling is also investigated using the 2005–2006 California CABG data set. The article provides theoretical and empirical evidence in choosing the right methodology for provider profiling.     

On Measuring Uncertainty of Benchmarked Predictors with Application to Disease Risk Estimate

Empirical Bayes (EB) estimates in general linear mixed models are useful for the small area estimation in the sense of increasing precision of estimation of small area means. However, one potential difficulty of EB is that the overall estimate for a larger geographical area based on a (weighted) sum of EB estimates is not necessarily identical to the corresponding direct estimate such as the overall sample mean. Another difficulty is that EB estimates yield over‐shrinking, which results in the sampling variance smaller than the posterior variance. One way to fix these problems is the benchmarking approach based on the constrained empirical Bayes (CEB) estimators, which satisfy the constraints that the aggregated mean and variance are identical to the requested values of mean and variance. In this paper, we treat the general mixed models, derive asymptotic approximations of the mean squared error (MSE) of CEB and provide second‐order unbiased estimators of MSE based on the parametric bootstrap method. These results are applied to natural exponential families with quadratic variance functions. As a specific example, the Poisson‐gamma model is dealt with, and it is illustrated that the CEB estimates and their MSE estimates work well through real mortality data.     

Delayed maturation in the colonial coralGoniastrea aspera (Scleractinia): whole-colony mortality, colony growth and polyp egg production

The present study examines (1) the cost of reproduction on colony growth, and (2) relationships among sexual maturity, whole-colony mortality rate and colony growth rate inGoniastrea aspera free from external influences by macrobenthos. Survival of colonies in permanent plots was followed for two years. Egg production by polyps in colonies collected just before the first spawning of a year was estimated by dissecting the polyps. Growth of the colonies (increase in number of polyps) was followed over one annual reproductive cycle. The cost of egg production on colony growth was apparent through colony ontogeny: (1) immature colonies had a greater annual growth rate than mature colonies, but produced almost no eggs; (2) in mature colonies, growth rate was negatively correlated with NE/PV (number of eggs per polyp volume mm^-3). Annual whole-colony mortality was high in colonies with fewer than11 polyps in initial colony size, while mortality was extremely low once a colony grew beyond this size. This critical size for low whole-colony mortality was much smaller than the colony size (40 polyps) which would attain maturity one year later. Age at maturity was estimated as six years. While survival to maturity may be a selective force for the evolution of delayed maturation, the present data suggest that high colony fecundity, achieved after a long growth period as an immature colony, and an abrupt decrease of colony growth rate after maturation are the crucial forces.     

Aboriginal women in rural Australia; a small study of infant feeding behaviour

BackgroundAboriginal women in rural areas have lower rates of breastfeeding than Australian averages. The reasons for this are poorly understood. Aboriginal people experience higher morbidity and increased rates of chronic disease throughout the life cycle. The protective effects of sustained breastfeeding could benefit rural Aboriginal communities.ObjectiveTo explore the factors impacting upon infant feeding choices in a rural Aboriginal Community.MethodsSemi-structured interviews were conducted with eight Aboriginal rural dwelling first time mothers. These women received a continuity of midwife and Aboriginal Health Worker model of care. Interviews were also undertaken with five Aboriginal Health Workers and two Aboriginal community breastfeeding champions. The analysis was integrated with a conventional literature review and was further developed and illustrated with historical literature. Indigenist methodology guided the study design, analysis and the dissemination of results.ResultsThree key themes were identified. These were “I’m doing the best thing for…” which encompasses the motivations underpinning infant feeding decisions; “this is what I know…” which explores individual and community knowledge regarding infant feeding; and “a safe place to feed” identifying the barriers that negative societal messages pose for women as they make infant feeding decisions. It appears loss of family and community breastfeeding knowledge resulting from colonisation still influences the Aboriginal women of today.DiscussionAboriginal women value and trust knowledge which is passed to them from extended family members and women within their Community. Cultural, historical and socioeconomic factors all strongly influence the infant feeding decisions of individuals in this study.ConclusionsEfforts to normalise breastfeeding in the culture of rural dwelling Aboriginal women and their supporting community appear to be necessary and may promote breastfeeding more effectively than optimal professional care of individuals can do.     

The assessment of parental stress and support in the neonatal intensive care unit using the Parent Stress Scale – Neonatal Intensive Care Unit

ProblemParental stress in the neonatal intensive care unit (NICU) has been reported, however identifying modifiable stress factors and looking for demographic parent factors related to stress has not been well researched.AimThis study aims to identify the most stressful elements for parents in the neonatal intensive care unit.MethodsParents of babies in an Australian neonatal intensive care unit (N = 73) completed both the Parent Stress Scale – Neonatal Intensive Care Unit and a survey of parent and baby demographic and support experience variables (Parent Survey) over an 18-month period.FindingsOlder parental age, very premature birth and twin birth were significantly associated with a higher Parent Stress Scale – Neonatal Intensive Care Unit score. Having a high score in the Relationship and Parental Role scale was strongly associated with attendance at the parent support group.ConclusionThese results indicate the variables associated with stress and this knowledge can be used by teams within hospitals to provide better supportive emotional care for parents.     

Single-parent households and mortality among children and youth

Although many studies have examined associations between family structure and child outcomes, few have considered how the increase in single-parent households since the 1960s may have affected child mortality rates. We examined state-level changes in the percentage of children living with single parents between 1968 and 2010 and state-level trends in mortality among children and youth (age 19 or younger) in the United States. Regression models with state and year fixed effects revealed that increases in single parenthood were associated with small increments in accidental deaths and homicides.     

Geographic Ancestry and Cause-specific Mortality in a National Population

There are marked differentials in mortality risks across regions in Finland. No exhaustive explanation to this variation has been provided, however. The aim of this paper is to analyse how geographic ancestry, as proxied by persons’ birth region and population group, interrelates with cause-specific mortality risks. Focusing on people aged between their mid-thirties and late-forties, we use longitudinal population register data that offer opportunities to account for variables that represent both persons’ social background and their own social status at young adult age. Results of Cox proportional hazard models say that these variables have substantial effects on mortality of different causes, but only a marginal impact on the variation in death rates by birth region and population group. The geographic mortality pattern is found to be specifically prominent for causes of death that are fairly unrelated to persons’ lifestyles. Our findings suggest that genetic predisposal as expressed in terms of geographic ancestry might play a relevant role in understanding mortality variation within the population of Finland.