bluuebunny/crossref_metadata_2025 huggingface dataset:
Context in the Risk Assessment of Digital Systems
Authors: Garrett Chris , Apostolakis George
Published: May 2006

As the use of digital computers for instrumentation and control of safety‐critical systems has increased, there has been a growing debate over the issue of whether probabilistic risk assessment techniques can be applied to these systems. This debate has centered on the issue of whether software failures can be modeled probabilistically. This paper describes a “context‐based” approach to software risk assessment that explicitly recognizes the fact that the behavior of software is not probabilistic. The source of the perceived uncertainty in its behavior results from both the input to the software as well as the application and environment in which the software is operating. Failures occur as the result of encountering some context for which the software was not properly designed, as opposed to the software simply failing “randomly.” The paper elaborates on the concept of “error‐forcing context” as it applies to software. It also illustrates a methodology which utilizes event trees, fault trees, and the Dynamic Flowgraph Methodology (DFM) to identify “error‐forcing contexts” for software in the form of fault tree prime implicants.
Mixed Levels of Uncertainty in Complex Policy Models
Authors: Casman Elizabeth A. , Morgan M. Granger , Dowlatabadi Hadi
Published: May 2006

The characterization and treatment of uncertainty poses special challenges when modeling indeterminate or complex coupled systems such as those involved in the interactions between human activity, climate and the ecosystem. Uncertainty about model structure may become as, or more important than, uncertainty about parameter values. When uncertainty grows so large that prediction or optimization no longer makes sense, it may still be possible to use the model as a “behavioral test bed” to examine the relative robustness of alternative observational and behavioral strategies. When modelsmust be run into portions of their phase space that are not well understood, different submodels may become unreliable at different rates. A common example involves running a time stepped model far into the future. Several strategies can be used to deal with such situations. The probability of model failure can be reported as a function of time. Possible alternative “surprises” can be assigned probabilities, modeled separately, and combined. Finally, through the use of subjective judgments, one may be able to combine, and over time shift between models, moving from more detailed to progressively simpler order‐of‐magnitude models, and perhaps ultimately, on to simple bounding analysis.
Decision‐Making with Heterogeneous Sources of Information
Authors: Richards Donald , Rowe William D.
Published: May 2006

In any model the values of estimates for various parameters are obtained from different sources each with its own level of uncertainty. When the probability distributions of the estimates are obtained as opposed to point values only, the measurement uncertainties in the parameter estimates may be addressed. However, the sources used for obtaining the data and the models used to select appropriate distributions are of differing degrees of uncertainty. A hierarchy of different sources of uncertainty based upon one's ability to validate data and models empirically is presented. When model parameters are aggregated with different levels of the hierarchy represented, this implies distortion or degradation in the utility and validity of the models used. Means to identify and deal with such heterogeneous data sourcesare explored, and a number of approaches to addressing this problem is presented. One approach, using Range/confidence Estimates coupled with an Information Value Analysis Process, is presented as an example.
A Survey of Approaches for Assessing and Managing the Risk of Extremes
Authors: Bier Vicki M. , Haimes Yacov Y. , Lambert James H. , Matalas Nicholas C. , Zimmerman Rae
Published: May 2006

In this paper, we review methods for assessing and managing the risk of extreme events, where “extreme events” are defined to be rare, severe, and outside the normal range of experience of the system in question. First, we discuss several systematic approaches for identifying possible extreme events. We then discuss some issues related to risk assessment of extreme events, including what type of output is needed (e.g., a single probability vs. a probability distribution), and alternatives to the probabilistic approach. Next, we present a number of probabilistic methods. These include : guidelines for eliciting informative probability distributions from experts; maximum entropy distributions; extreme value theory; other approaches for constructing prior distributions (such as reference or noninformative priors); the use of modeling and decomposition to estimate the probability (or distribution) of interest; and bounding methods. Finally, we briefly discuss several approaches for managing the risk of extreme events, and conclude with recommendations and directions for future research.
Combining Probability Distributions From Experts in Risk Analysis
Authors: Clemen Robert T. , Winkler Robert L.
Published: May 2006

This paper concerns the combination of experts' probability distributions in risk analysis, discussing a variety of combination methods and attempting to highlight the important conceptual and practical issues to be considered in designing a combination process in practice. The role of experts is important because their judgments can provide valuable information, particularly in view of the limited availability of “hard data” regarding many important uncertainties in risk analysis. Because uncertainties are represented in terms of probability distributions in probabilistic risk analysis (PRA), we consider expert information in terms of probability distributions. The motivation for the use of multiple experts is simply the desire to obtain as much information as possible. Combining experts' probability distributions summarizes the accumulated information for risk analysts and decision‐makers. Procedures for combining probability distributions are often compartmentalized as mathematical aggregation methods or behavioral approaches, and we discuss both categories. However, an overall aggregation process could involve both mathematical and behavioral aspects, and no single process is best in all circumstances. An understanding of the pros and cons of different methods and the key issues to consider is valuable in the design of acombination process for a specific PRA. The output, a ”combined probabilitydistribution,” can ideally be viewed as representing a summary of the current state of expert opinion regarding the uncertainty of interest.
Public Support For Earthquake Risk Mitigation In Portland, Oregon
Authors: Flynn James , Slovic Paul , Mertz C. K. , Carlisle Cathie
Published: May 2006

During the 1980s, seismic research suggested that Oregon and the City of Portland had a higher risk of a major earthquake than had previously been assumed. In 1993, the State of Oregon adopted a new version of the Oregon Structural Specialty Code, which changed the designation of western Oregon from seismic zone 2b to seismic zone 3. The City of Portland established a program and a Task Force on Seismic Strengthening of Buildings to recommend actions that would encourage upgrading of city buildings. A survey of adult city residents was conducted in April, 1996 to determine public attitudes and opinions about earthquake risks, management and mitigation of earthquake hazards, priorities for protection by strengthening buildings, evaluations of strategies for informing the public about earthquake risks, and support for specific options the city might take to protect citizens against earthquake events. Social and demographic information on individuals and households was also collected. Respondents provided ratings for a wide range of social and environmental risks, provided information on priorities for strengthening key buildings and infrastructure facilities, and answered hypothetical questions about voting for bond measures to pay for city earthquake mitigation programs. Respondents recognized significant risk from earthquakes and supported programs to protect people, especially vulnerable residents such as children and the sick. There was strong support for protecting emergency response capabilities. There was much less support for using public funds to reduce the risks associated with privately owned buildings. There were also some strong pockets of resistance to publicly funded mitigation programs in response to the hypothetical bond measures.
Exposure to Environmental Tobacco Smoke in the Workplace and the Impact of Away‐From‐Work Exposure
Authors: LaKind Judy S. , Graves Carol G. , Ginevan Michael E. , Jenkins Roger A. , Naiman Daniel Q. , Tardiff Robert G.
Published: May 2006

Concentrating on exposure in workplaces where smoking occurs, we examined environmental tobacco smoke (ETS)‐related concentration data from the 16‐City This study.(1,2) This study involved a large population of nonsmokers, used personal monitors, and encompassed a wide selection of ETS‐related constituents. This first article in a series of three describes the 16‐City Study, considers the impact of demographic variables, and concludes that these variables did not explain differences in exposure to ETS. We compared 16‐City Study concentrations obtained in the workplace to previously reported workplace concentrations and determined that data from this study were representative of current ETS exposure in nonmanufacturing workplaces where smoking occurs. Considering factors other than demographic factors, we found that, not surprisingly, the number of cigarettes observed in the workplace had an impact on exposure concentrations. Finally, we compared people from homes where smoking occurs with people from nonsmoking homes and found that people from smoking homes observed more smoking in the workplace and experienced higher concentrations of ETS‐related compounds in the workplace, even when they observed the same number of cigarettes being smoked in the workplace. In two subsequent articles in this series, we discuss relationships between various ETS markers and provide estimates of distributions of doses to nonsmoking workers employed in workplaces where smoking occurs.
A Comparison of Methods of Benchmark‐Dose Estimation for Continuous Response Data
Authors: West R. Webster , Kodell Ralph L.
Published: May 2006

Methods of quantitative risk assessment for toxic responses that are measured on a continuous scale are not well established. Although risk‐assessment procedures that attempt to utilize the quantitative information in such data have been proposed, there is no general agreement that these procedures are appreciably more efficient than common quantal dose‐response procedures that operate on dichotomized continuous data. This paper points out an equivalence between the dose‐response models of the nonquantal approach of Kodell and West(1)) and a quantal probit procedure, and provides results from a Monte Carlo simulation study to compare coverage probabilities of statistical lower confidence limits on dose corresponding to specified additional risk based on applying the two procedures to continuous data from a dose‐response experiment. The nonquantal approach is shown to be superior, in terms of both statistical validity and statistical efficiency.
Risk Assessment Based on Financial Data: Market Response to Airline Accidents
Authors: Dillon Robin L. , Johnson Blake E. , Patè‐Cornell M. Elisabeth
Published: May 2006

The risk of catastrophic failures, for example in the aviation and aerospace industries, can be approached from different angles (e.g., statistics when they exist, or a detailed probabilistic analysis of the system). Each new accident carries information that has already been included in the experience base or constitutes new evidence that can be used to update a previous assessment of the risk. In this paper, we take a different approach and consider the risk and the updating from the investor's point of view. Based on the market response to past airplane accidents, we examine which ones have created a “surprise response” and which ones are considered part of the risk of the airline business as previously assessed. To do so, we quantify the magnitude and the timing of the observed market response to catastrophic accidents, and we compare it to an estimate of the response that would be expected based on the true actual cost of the accident including direct and indirect costs (“full‐cost information” response). First, we develop a method based on stock market data to measure the actual market response to an accident and we construct an estimate of the “full‐cost information” response to such an event. We then compare the two figures for the immediate and the long‐term response of the market for the affected firm, as well as for the whole industry group to which the firm belongs. As an illustration, we analyze a sample of ten fatal accidents experienced by major US domestic airlines during the last seven years. In four cases, we observed an abnormal market response. In these instances, it seems that the shareholders may have updated their estimates of the probability of a future accident in the affected airlines or more generally of the firm's future business prospects. This market reaction is not always easy to explain much less to anticipate, a fact which management should bear in mind when planning a firm's response to such an event.
Exposure to Persistent Organochlorines in Canadian Breast Milk A Probabilistic Assessment
Authors: Hoover Sara M.
Published: May 2006

Exposure to persistent organochlorines in breast milk was estimated probabilistically for Canadian infants. Noncancer health effects were evaluated by comparing the predicted exposure distributions to published guidance values. For chemicals identified as potential human carcinogens, cancer risks were evaluated using standard methodology typically applied in Canada, aswell as an alternative method developed under the Canadian Environmental Protection Act. Potential health risks associated with exposure to persistentorganochlorines were quantitatively and qualitatively weighed against the benefits of breast‐feeding. Current levels of the majority of contaminants identified in Canadian breast milk do not pose unacceptable risks to infants. Benefits of breast‐feeding are well documented and qualitatively appear to outweigh potential health concerns associated with organochlorine exposure. Furthermore, the risks of mortality from not breast‐feeding estimated by Rogan and colleagues exceed the theoretical cancer risks estimated for infant exposure to potential carcinogens in Canadian breast milk. Although levels of persistent compounds have been declining in Canadian breast milk, potentially significant risks were estimated for exposure to polychlorinatedbiphenyls, dibenzo‐p‐dioxins, and dibenzofurans. Follow‐up work is suggested that would involve the use of a physiologically based toxicokinetic modelwith probabilistic inputs to predict dioxin exposure to the infant. A more detailed risk analysis could be carried out by coupling the exposure estimates with a dose‐response analysis that accounts for uncertainty.
Evaluation of the Uncertainty in an Oral Reference Dose for Methylmercury Due to Interindividual Variability in Pharmacokinetics
Authors: Clewell Harvey J. , Gearhart Jeffery M. , Gentry P. Robinan , Covington Tammie R. , VanLandingham Cynthia B. , Crump Kenny S. , Shipp Annette M.
Published: May 2006

An analysis of the uncertainty in guidelines for the ingestion of methylmercury (MeHg) due to human pharmacokinetic variability was conducted using a physiologically based pharmacokinetic (PBPK) model that describes MeHg kinetics in the pregnant human and fetus. Two alternative derivations of an ingestion guideline for MeHg were considered: the U.S. Environmental Protection Agency reference dose (RfD) of 0.1 pg/kg/day derived from studies of an Iraqi grain poisoning episode, and the Agency for Toxic Substances and Disease Registry chronic oral minimal risk level (MRL) of 0.5 pglkglday based on studies of a fisheating population in the Seychelles Islands. Calculation of an ingestion guideline for MeHg from either of these epidemiological studies requires calculation of a dose conversion factor (DCF) relating a hair mercury concentration to a chronic MeHg ingestion rate. To evaluate the uncertainty in this DCF across the population of U.S. women of child‐bearing age, Monte Carlo analyses were performed in which distributions for each of the parameters in the PBPK model were randomly sampled lo00 times. The 1st and 5th percentiles of the resulting distribution of DCFs were a factor of 1.8 and 1.5 below the median, respectively. This estimate of variability is consistent with, but somewhat less than, previous analyses performed with empirical, one‐compartment pharmacokinetic models. The use of a consistent factor in both guidelines of 1.5 for pharmacokinetic variability in the DCF, and keeping all other aspects of the derivations unchanged, would result in an RfD of 0.2 pglkglday and an MRL of 0.3 pglkglday.
Estimating Risk Assessment Exposure Point Concentrations when the Data Are Not Normal or Lognormal
Authors: Schulzl Terry W. , Griffin Susan
Published: May 2006

The US. Environmental Protection Agency (EPA) recommends the use of th one‐sided 95% upper confidence limit of the arithmetic mean based on eithe a normal or lognormal distribution for the contaminant (or exposure point) concentration term in the Superfund risk assessment process. When the data are not normal or lognormal this recommended approach may overestimate the exposure point concentration (EPC) and may lead to unecessary cleanup at a hazardous waste site. The EPA concentration term only seems to perform lik alternative EPC methods when the data are well fit by a lognormal distribution. Several alternative methods for calculating the EPC are investigated and compared using soil data collected from three hazardous waste sites in Montana, Utah, and Colorado. For data sets that are well fit by a lognormal distribution, values for the Chebychev inequality or the EPA concentration term may be appropriate EPCs. For data sets where the soil concentration data are well fit by gamma distributions, Wong's method may be used for calculating EPCs. The studentized bootstrap‐tand Hall's bootstrap‐ttransformation are recommended for EPC calculation when all distributionfits are poor. If a data set is well fit by a distribution, parametric bootstrap may provide a suitable EPC.
Bayesian Forecasting via Deterministic Model
Authors: Krzysztofowicz Roman
Published: May 2006

Rational decision making requires that the total uncertainty about a variate of interest (a predictand) be quantified in terms of a probability distribution, conditional on all available information and knowledge. Supposethe state‐of‐knowledge is embodied in a deterministic model, which is imperfect and outputs only an estimate of the predictand. Fundamentals are presented of two Bayesian methods for producing a probabilistic forecast via anydeterministic model. The Bayesian Processor of Forecast (BPF) quantifies the total uncertainty in terms of a posterior distribution, conditional on model output. The Bayesian Forecasting System (BFS) decomposes the total uncertainty into input uncertainty and model uncertainty, which are characterized independently and then integrated into a predictive distribution. The BFS is compared with Monte Carlo simulation and “ensemble forecasting” technique, none of which can alone produce a probabilistic forecast that quantifies the total uncertainty, but each can serve as a component of the BFS.
A Perspective on Nuclear Waste
Authors: North D. Warner
Published: May 2006

The management of spent nuclear fuel and high‐level nuclear waste has the deserved reputation as one of the most intractable policy issues facing the United States and other nations using nuclear reactors for electric power generation. This paper presents the author's perspective on this complexissue, based on a decade of service with the Nuclear Waste Technical ReviewBoard and Board on Radioactive Waste Management of the National Research Council.
Historical Relationship Between Performance Assessment for Radioactive Waste Disposal and Other Types of Risk Assessment
Authors: Rechard Rob P.
Published: May 2006

This article describes the evolution of the process for assessing the hazards of a geologic disposal system for radioactive waste and, similarly, nuclear power reactors, and the relationship of this process with other assessments of risk, particularlyassessments of hazards from manufactured carcinogenic chemicals during use and disposal. This perspective reviews the common history of scientific concepts for risk assessment developed until the 1950s. Computational tools and techniques developed in the late 1950s and early 1960s to analyze the reliability of nuclear weapon delivery systems were adopted in the early 1970s for probabilistic risk assessment of nuclear power reactors, a technology for which behavior was unknown. In turn, these analyses became an important foundation for performance assessment of nuclear waste disposal in the late 1970s. The evaluation of risk to human health and the environment from chemical hazards is built on methods for assessing the dose response of radionuclides in the1950s. Despite a shared background, however, societal events, often in the form of legislation, have affected the development path for risk assessment for human health, producing dissimilarities between these risk assessments and those for nuclear facilities. An important difference is the regulator's interest in accounting for uncertainty.
Development of a Performance Assessment Capability in the Waste Management Programs of the U.S. Nuclear Regulatory Commission
Authors: Eisenberg Norman A. , Lee Michael P. , McCartin Timothy J. , McConnell Keith I. , Thaggard Mark , Campbell Andrew C.
Published: May 2006

The U.S. Nuclear Regulatory Commission (NRC) staff has developed a performance assessment capability to address three programmatic areas in nuclear waste management: high‐level waste, low‐level waste, and decommissioning of licensed facilities (license termination). The NRC capability consists of (1) methodologies for performance assessment; (2) models and computer codes for estimating system performance; (3) regulatory guidance in various forms, such as regulations, Branch Technical Positions, and Standard Review Plans; and (4) a technical staff experienced in executing and evaluating performance assessments for a variety of waste systems. Although the tools and techniques are refined for each programmatic area, general approaches and similar issues are encountered in all areas.
Residential Building Codes, Affordability, and Health Protection: A Risk‐Tradeoff Approach
Authors: Hammitt James K. , Belsky Eric S. , Levy Jonathan I. , Graham John D.
Published: May 2006

Residential building codes intended to promote health and safety may produce unintended countervailing risks by adding to the cost of construction. Higher construction costs increase the price of new homes and may increase health and safety risks through “income” and “stock” effects. The income effect arises because households that purchase a new home have less income remaining for spending on other goods that contribute to health and safety. The stock effect arises because suppression of new‐home construction leads to slower replacement of less safe housing units. These countervailing risks are not presently considered in code debates. We demonstrate the feasibility of estimating the approximate magnitude of countervailing risks by combining the income effect with three relatively well understood and significant home‐health risks. We estimate that a code change that increases the nationwide cost of constructing and maintaining homes by $150 (0.1% of the average cost to build a single‐family home) would induce offsetting risks yielding between 2 and 60 premature fatalities or, including morbidity effects, between 20 and 800 lost quality‐adjusted life years (both discounted at 3%)each year the code provision remains in effect. To provide a net health benefit, the code change would need to reduce risk by at least this amount. Future research should refine these estimates, incorporate quantitative uncertainty analysis, and apply a full risk‐tradeoff approach to real‐world casestudies of proposed code changes.
An Evaluation of Risk Estimation Procedures for Mixtures of Carcinogens
Authors: Hwang Jing‐Shiang , Chen James J.
Published: May 2006

The estimation of health risks from exposure to a mixture of chemical carcinogens is generally based on the combination of information from several available single compound studies. The current practice of directly summing the upper bound risk estimates of individual carcinogenic components as an upper bound on the total risk of a mixture is known to be generally too conservative. Gaylor and Chen (1996, Risk Analysis) proposed a simple procedure to compute an upper bound on the total risk using only the upper confidence limits and central risk estimates of individual carcinogens. The Gaylor‐Chen procedure was derived based on an underlying assumption of the normality for the distributions of individual risk estimates. In this paper we evaluated the Gaylor‐Chen approach in terms of the coverage probability. The performance of the Gaylor‐Chen approach in terms the coverages of the upper confidence limits on the true risks of individual carcinogens. In general, if the coverage probabilities for the individual carcinogens are all approximately equal to the nominal level, then the Gaylor‐Chen approach shouldperform well. However, the Gaylor‐Chen approach can be conservative or anti‐conservative if some or all individual upper confidence limit estimates are conservative or anti‐conservative.
Ethylene Oxide Cancer Risk Assessment Based on Epidemiological Data: Application of Revised Regulatory Guidelines
Authors: Teta M. Jane , Sielken Robert L. , Valdez‐Flores Ciriaco
Published: May 2006

Ethylene oxide (EO) research has significantly increased since the 1980s, when regulatory risk assessments were last completed on the basis of theanimal cancer chronic bioassays. In tandem with the new scientific understanding, there have been evolutionary changes in regulatory risk assessment guidelines, that encourage flexibility and greater use of scientific information. The results of an updated meta‐analysis of the findings from 10 unique EO study cohorts from five countries, including nearly 33,000 workers, and over 800 cancers are presented, indicating that EO does not cause increased risk of cancers overall or of brain, stomach or pancreatic cancers. The findings for leukemia and non‐Hodgkin's lymphoma (NHL) are inconclusive. Two studies with the requisite attributes of size, individual exposure estimates and follow up are the basis for dose‐response modeling and added lifetime risk predictions under environmental and occupational exposure scenariosand a variety of plausible alternative assumptions. A point of departure analysis, with various margins of exposure, is also illustrated using human data. The two datasets produce remarkably similar leukemia added risk predictions, orders of magnitude lower than prior animal‐based predictions under conservative, default assumptions, with risks on the order of 1 × 10−6 or lower for exposures in the low ppb range. Inconsistent results for “lymphoid” tumors, a non‐standard grouping using histologic information from death certificates, are discussed. This assessment demonstrates the applicability of the current risk assessment paradigm to epidemiological data.
Using Animated Probability Plots to Explore the Suitability of Mixture Models with Two Component Distributions
Authors: Burmaster David E. , Thompson Kimberly M.
Published: May 2006

Risk assessors often use different probability plots as a way to assessthe fit of a particular distribution or model by comparing the plotted points to a straight line and to obtain estimates of the parameters in parametric distributions or models. When empirical data do not fall in a sufficiently straight line on a probability plot, and when no other single parametricdistribution provides an acceptable (graphical) fit to the data, the risk assessor may consider a mixture model with two component distributions. Animated probability plots are a way to visualize the possible behaviors of mixture models with two component distributions. When no single parametric distribution provides an adequate fit to an empirical dataset, animated probability plots can help an analyst pick some plausible mixture models for the data based on their qualitative fit. After using animations during exploratory data analysis, the analyst must then use other statistical tools, including but not limited to: Maximum Likelihood Estimation (MLE) to find the optimal parameters, Goodness of Fit (GoF) tests, and a variety of diagnostic plots to check the adequacy of the fit. Using a specific example with two LogNormal components, we illustrate the use of animated probability plots asa tool for exploring the suitability of a mixture model with two component distributions. Animations work well with other types of probability plots, and they may be extended to analyze mixture models with three or more component distributions.
After VaR: The Theory, Estimation, and Insurance Applications of Quantile‐Based Risk Measures
Authors: Dowd Kevin , Blake David
Published: May 2006

Abstract

We discuss a number of quantile‐based risk measures (QBRMs) that have recently been developed in the financial risk and actuarial/insurance literatures. The measures considered include the Value‐at‐Risk (VaR), coherent risk measures, spectral risk measures, and distortion risk measures. We discuss and compare the properties of these different measures, and point out that the VaR is seriously flawed. We then discuss how QBRMs can be estimated, and discuss some of the many ways they might be applied to insurance risk problems. These applications are typically very complex, and this complexity means that the most appropriate estimation method will often be some form of stochastic simulation.
Strategic Demand for Insurance
Authors: Seog S. Hun
Published: May 2006

Abstract

We focus on the corporate demand for insurance under duopoly. We consider the case in which firms purchase insurance in order to enhance their competitiveness. We show that a higher level of corporate insurance makes a firm more aggressive and its competitor less aggressive in the output market (strategic effect). The optimal coverage of insurance is determined by comparing the strategic effect of insurance and the cost of insurance. The optimal coverage is positive if the strategic effect is greater than the cost of insurance. An interesting implication is that a risk‐neutral firm may purchase actuarially unfair insurance. The main strategic effect of insurance comes from the fact that firms purchase insurance before they produce outputs. Insurance makes firms more aggressive due to the limited risk costs of firms.
The Effects of Occupational Injuries After Returns to Work: Work Absences and Losses of On‐the‐Job Productivity
Authors: Butler Richard J. , Baldwin Marjorie L. , Johnson William G.
Published: May 2006

Abstract

We extend the research on postinjury employment by estimating productivity losses for workers with permanent partial disabilities (PPDs) in the first three years after injury. Our method distinguishes between productivity losses attributed to spells of work absence versus reduced earnings during spells of employment. The method is applied to data for 800 Ontario workers with PPDs. The results document large productivity losses persisting at least three years after injury, with different loss patterns for workers returning to stable versus unstable employment. Human capital investments or job accommodations can reduce productivity losses, but the significant determinants of losses differ for the stable versus unstable employment groups.
Microstructural Evolution of Crystalline‐Oriented (K0.5Na0.5)NbO3 Piezoelectric Ceramics with a Sintering Aid of CuO
Authors: Takao Hisaaki , Saito Yasuyoshi , Aoki Yoshifumi , Horibuchi Kayo
Published: May 2006

The microstructural development of crystalline‐oriented (K0.5Na0.5)NbO3 (KNN)‐based piezoelectric ceramics during sintering was investigated. The addition of CuO as a sintering aid was found to be effective for fabricating highly oriented and dense KNN ceramics. KNN specimens containing 0.5–1.0 mol% CuO sintered at 1100°C for 1 h were found to have relative densities and pseudo‐cubic {100} orientation degrees of 95% or higher. In the early stages of sintering, KNN is formed in the reaction between complementary reactants NaNbO3 and KNbO3, after which oriented grain growth proceeds at a relative density of more than 90%. In addition, the results of transmission electron microscopy observation showed that textured KNN ceramics have a unique pectinate‐like domain structure with domain walls consisting of {101} planes.
Contact lens‐related corneal ulcers requiring hospitalization: A 7‐year retrospective study in Belgium
Authors: Verhelst Dominik , Koppen Carina , Van Looveren Jan , Meheus André , Tassignon Marie‐José ,   the Belgian Keratitis Study Group
Published: May 2006

Purpose:  To evaluate the clinical and epidemiological aspects of contact lens‐related infectious corneal ulcers requiring hospitalization.

Methods:  A retrospective analysis was performed on the files of patients hospitalized for contact lens‐induced corneal ulcer in the eight Belgian university hospitals over a 7‐year period (January 1997 to December 2003). Diagnoses for all hospitalized patients are obligatorily registered using the ICD‐9 code.

Results:  A total of 107 patients with contact lens‐related corneal ulcers were documented: the number increased from five in 1997 to 22 in 2003. A total of 99 subjects used soft contact lenses, of whom nine used disposables, 73 planned replacement and 17 conventional lenses. Only six patients used extended wear lenses. Three patients used daily disposable lenses. The most frequently cultured organisms were Pseudomonas and other Gram‐negative germs (70%) and Acanthamoeba (16%). The majority (77%) of the corneal ulcerations were centrally located and resulted in an average visual loss of four lines.

Conclusion:  During the study period, the number of patients hospitalized rose, which is only partially explained by the increasing prevalence of lens wearers: 3.5% and 6.5% of the Belgian population used lenses in 1995 and 2003, respectively. These factual data highlight the need for improvements in patient education.
Retrobulbar haemodynamics and contrast sensitivity improvements after CO2 breathing
Authors: Huber Klaudia K. , Adams Herbert , Remky Andreas , Arend Kay O.
Published: May 2006

Purpose:  Effects of gas mixtures have been widely studied. Carbon dioxide (CO2) is known to act as a vasodilator, whereas oxygen (O2) acts as a vasoconstrictor. Therefore, the interpretation of results is difficult. In this study, only the effect of an elevated CO2 level on retrobulbar hemodynamics and contrast sensitivity was investigated.

Methods:  Thirty adults (age 31 ± 7) were examined under normocapnic and hypercapnic conditions. Colour Doppler imaging was used to measure the velocity in the ophthalmic and central retinal artery. Moreover, contrast sensitivity using the CSV‐1000 was investigated. Blood pressure, heart rate and intraocular pressure (IOP) were measured and ocular perfusion was calculated.

Results:  Under hypercapnia, mean end tidal CO2 increased from 36.4 mmHg to 42.5 mmHg and blood oxygen saturation increased from 98.3% to 98.6% (p < 0.0001). Hypercapnia significantly reduced IOP by 0.94 mmHg (p < 0.0008). In the central retinal artery, the mean PSV increased by 18% (p < 0.0001) and the mean EDV by 21% (p = 0.0054). In the ophthalmic artery, the mean PSV increased by 13% (p < 0.0001) and the mean EDV by 26% (p = 0.0002). Furthermore, there was a significant increase of contrast sensitivity (spatial frequency: 3cpd: p = 0.0016; 6cpd: p = 0.005; 12cpd: p = 0.0012). Systolic blood pressure (p = 0.0225), mean arterial blood pressure (p = 0.0097) and ocular perfusion pressure (p = 0.0013) increased significantly.

Conclusion:  This setting was able to detect an increase in blood flow velocity in normal subjects under hypercapnia. Furthermore, hypercapnia results in a functional improvement in contrast sensitivity, possible due to the increased blood flow or the increase in blood oxygen levels.
Caries development after substitution of supervised fluoride rinses and tooth brushings by unsupervised use of fluoride toothpaste
Authors: Karjalainen Sára , Eriksson Anna‐Leena , Ruokola Mauno , Toivonen Arja
Published: May 2006

Abstract In a nonfluoridated community of Finland, where fortnightly fluoride rinsing with 0.2% sodium fluoride has been used for nearly two decades, a total of 313 children 7–8 yr old were recruited and randomly divided into two groups. 206 children completed the 3‐yr trial. The control group (n=94) participated in the rinsing program which included supervised toothbrushings, while the test group (n= 112) received a new fluoride toothpaste tube (0.15% F) for home use every second month. Annual dental recordings, treatment plannings and the treatment itself were all carried out by one clinician. At the end of the study the number of caries‐free children of the toothpaste group was lower (P<0.01) and the caries increment higher (<0.05) than that of the mouthrinse group. Out of the mean of four dental visits per child and year some 1.5 were prophylactic by nature. No differences were found between the number of treatment visits, time or prophylactic care of the two groups. Unsupervised use of fluoride toothpaste may not be a sufficient substitute for the school‐based fortnightly fluoride rinses and supervised toothbrushings in caries prevention of children with erupting permanent teeth.
The Hong Kong Adult Oral Health Survey – 1991: background, study population, and methods
Authors: Schwarz Eli , Lo Edward C. M. , Corbet Esmonde F. , Holmgren Christopher J. , Lim L. P. , Davies W. Ian R.
Published: May 2006

Abstract This second adult oral health survey was conducted with the following main aims: 1) to describe the oral health conditions and to analyse the oral health care needs and demands of 65–74‐yr‐olds in Hong Kong, and to propose appropriate strategies for meeting their needs in the light of societal obligations; 2) to describe the oral health conditions and to analyse the oral health care needs and demands of 35–44‐yr‐oIds in Hong Kong with special emphasis on assessment of changes in this age group since 1984 (when the first adult oral health survey was conducted); 3) to assess the impact of sociodemographic and dental care system factors on the oral health status of selected adult age groups: and 4) to utilize survey data to refine curriculum development and research strategies in the Faculty of Dentistry, as well as in the proposal of appropriate action to governmental committees on dental health policy. For enhanced comparability with the previous study, the 35–44‐yr‐olds were selected from the same geographic areas of Hong Kong Island. Multistage cluster sampling was used to recruit the study population, defined geographic units and addresses being used as the starting‐point. A sample of 398 subjects was selected, of whom 93% were both interviewed and clinically examined. The 65–74‐yr‐olds were recruited from housing estates in all principal areas of Hong Kong, yielding a sample of 559 subjects, of whom 96% were both interviewed and clinically examined. The analysis of the data was based on the model used by the International Collaborative Study II, from which other methodologic guidance had been sought. The definitions of selected sociodemographic variables such as occupation, income, Family Material Possession Index, family support, and dental anxiety, which are relevant to the whole study, are given here.
Tooth and root conditions in the middle‐aged and the elderly in Hong Kong
Authors: Lo Edward C. M. , Schwarz Eli
Published: May 2006

Abstract In an oral health survey of Hong Kong Chinese conducted in 1991, a sample of 372 35–44‐yr‐olds and 537 noninstitutionalized 65–74‐yr‐olds were interviewed and clinically examined. The examination procedures, instruments, and diagnostic criteria used to detect coronal caries followed those recommended by the World Health Organization (1987). The diagnostic criteria used to assess root‐surface caries were based on those used in a national oral health survey of US employed adults (National Institute of Denial Research. 1987). Calibration of examiners was conducted before the survey and the interexaminer reliability was found to be very high; the kappa statistics were 0.93 and 0.91 for the younger and older age groups, respectively. None of the 35–44‐yr‐olds were edentulous and 96% had 21 teeth or more. The prevalence of edentulousness among the elderly was 12%. The DMFT indices of the younger and older age groups were 8.7 and 18.9, respectively. In both age groups, MT was the major component of the DMFT index, and female subjects had a slightly higher score. The prevalences of decayed/filled roots were 7% and 26%i for the 35–44‐ and 65–74‐yr‐olds, respectively. As compared with previous surveys conducted in Hong Kong, there has been a 40% reduction in the DMFT index of the 35–44‐yr‐olds since 1968, but little change in the tooth and root conditions was noted between 1984 and 1991.
Oral mucosal lesions in 65–74‐year‐old Hong Kong Chinese
Authors: Corbet Esmonde F. , Holmgren Christopher J. , Philipsen Hans P.
Published: May 2006

Abstract There have been no reported surveys of oral mucosal lesions among the elderly in Asian countries. Therefore, the purpose of this study was to determine the prevalence of oral mucosal lesions among 65–74‐yr‐old, community‐dwelling elderly Chinese in Hong Kong and to determine the prevalence of lesions in denture wearers, tobacco smokers, and alcohol drinkers. A total of 537 noninstitutionalized 65–74‐yr‐olds were interviewed and clinically examined in an oral health survey conducted in 1991. In the survey, the elderly underwent a systematic examination of their oral mucosa by one of the three examiners with the aid of an overhead light. The examiners were trained and calibrated before and during the survey, and a specially prepared colour atlas of oral mucosal lesions was used for lesion recognition. No mucosal lesions were detected in 64% of the elderly. In the 193 elderly subjects with lesions, 80% exhibited only one lesion. There was no difference in prevalence between men and women. The more common lesions, each being found in 5–7% of the elderly, were lingual varicosities, frictional keratosis on the buccal mucosa, denture stomatitis on the palatal mucosa, and denture‐induced hyperplasia in the maxillary and mandibular buccal sulcus. Denture wearers had a higher prevalence of lesions (40%) than nonwearers (32%). There was no difference in the prevalence or number of oral mucosal lesions between those defined as users of tobacco and alcohol and those defined as nonusers in this study. No confirmed oral malignancies were found.
Prevalence and distribution of developmental enamel defects in primary dentition of Chinese children 3–5 years old
Authors: Li Yihong , Navia Juan M. , Bian Jin‐You
Published: May 2006

Abstract A total of 1344 children, 3–5 yr old, from two rural counties, Haidian and Miyun, close to Beijing, China, were examined in 1992. A modified DDE Index was employed in this study, and a pre‐designed formula was used to calculate an enamel detect score (EDS) for each individual in the study. Oral examination was performed by one dentist under natural light using a standard mouth mirror and dental probe. Developmental enamel lesions were diagnosed without drying or cleaning the teeth prior to examination. Results from this study showed that primary teeth with defective enamel were seen in 23.9% of the children examined, opacity in 1.6%, and hypoplasia in 22.2%. Among the teeth, maxillary central and lateral incisors were affected by enamel hypoplasia most often (40.8% and 39.2%), followed by maxillary canines (25.7%), maxillary 1st molars (22.1%), and mandibular 1st molars (18.5%). The enamel defects occurred more frequently on the buccal surfaces of teeth than on any other surface. The study did not find a significant association of the children's age, family socioeconomic status, and anthropometric measurements with the distribution of enamel defects. However, there was a significantly higher prevalence of teeth with defects in males compared to females (P < 0.001), as well as mean tooth surfaces with defects (P < 0.05), and mean EDS (P < 0.05). Children born prematurely were shown to have four times more enamel lesions than children who were full term (P < 0.01). Children with low birth weight also showed a statistically significant higher prevalence of enamel defects (P < 0.05) and a greater severity of hypoplastic lesions measured by EDS (P < 0.05) than those with normal birth weight. The results indicate that nutrition during fetal development is important in determining normal development of enamel in primary teeth. Nutritional status (diagnosed by anthropometric measurements) after the critical period was not associated with enamel defects induced earlier in life. The study suggested, therefore, that nutrition is important for maintaining proper development of the teeth only during the critical period when teeth are susceptible to the formation of defects.
Evaluation of screening for oral cancer and precancer in a company headquarters
Authors: Downer M. C. , Evans A. W. , Hallett C. M. Hughes , Jullien J. A. , Speight P. M. , Zakrzewska J. M.
Published: May 2006

Abstract Oral cancer and precancer appear to fulfil many of the criteria for a disease suitable for mass screening. Several commercial organisations in the UK have introduced screening for their employees. One program has been formally evaluated over the course of 1 yr. Of 553 company headquarters staff aged ≥40 yr, 292 (53%) responded to the well‐publicised screening invitation and received a simple clinical examination of the oral mucosa from one of two company dentists. In addition, 17 staff were screened from a separate company work‐site. After screening, subjects were examined independently by an oral medicine specialist with access to the relevant diagnostic aids. The dentists' screening decisions were validated against the specialist's definitive diagnoses (the‘gold standard'). The true prevalence of subjects with lesions diagnosed as positive (white patch, red patch or ulcer of greater than 2 weeks' duration) was 17 (5.5%). Overall, sensitivity was 0.71 and specificity, 0.99. The compliance rate to screening among headquarters subjects in seven occupational categories did not differ significantly from the occupational profile for all headquarters personnel. Estimates of relative risk of a positive diagnosis were calculated by logistic regression for five independent variables: gender, age, moderate smoking, heavy smoking, and smoking combined with greater than low risk alcohol consumption. Only heavy smoking (≥20 cigarettes per day) produced a significant odds ratio (3.43, P < 0.05).