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PubMed2003

Complete curve fitting of extraction profiles for estimating uncertainties in recovery estimates.

This paper reports the use of improved numerical approaches to modelling extraction profiles, and shows that the approach substantially reduces statistical prediction uncertainties compared to those obtained on the basis of a three-point extrapolation from the later part of the extraction curve. Numerical fitting of manually obtained polycyclic aromatic hydrocarbon extraction data to a spherical particle diffusion model showed uncertainties typically reduced by a factor of three (with extremes at 1.02 and 770). Application to pressurised fluid extraction study of pelletised poly(vinylchloride) containing 30 mass% di(2-ethylhexyl)phthalate also showed good improvements. However, this high precision data showed small but significant lack of fit resulting in residual correlation and visibly biased prediction (more so than simple extrapolation). Re-fitting and uncertainty estimation using a first-order autoregression approximation to the covariance matrix produced more realistic uncertainty estimates and closer parameter estimates and is accordingly recommended for treating residual correlation from other causes, but did not entirely alleviate the problem. Different shape models (spherical, plane sheet and cylindrical) were applied without accounting fully for fitting error, and particle size effects were eliminated by modelling a simple size distribution. However, an approximate model based on linearly concentration-dependent diffusion coefficient showed excellent fit, confirming concentration-dependence as the most likely cause. This semiempirical model led to an uncertainty in total extractable material, at 0.2% of the total extractable value (with allowance for correlation). This is potentially good enough for recovery estimation and correction in certification of reference materials for validation purposes.

Journal Article↗

PubMed1995

Effects of signal and masker uncertainty on children's detection.

This paper reports the results of two experiments that examined the effects of signal and masker uncertainty on preschool-age children's and adults' detection of tonal signals in noise maskers. In Experiment 1 (signal uncertainty) the signal was randomly at 501 or 2818 Hz. The majority of the adult listeners showed a slight decrement in performance consistent with an ability to monitor both frequencies simultaneously. The majority of the children, however, showed no decrement in performance, suggesting that the children may not have focused attention at the signal frequency even when it was fixed. In Experiment 2 (masker uncertainty), random-frequency, random-level, tonal distracters were added to each interval of the 2 alternative-forced-choice (2afc) procedure. The effect of masker uncertainty was much larger than that of signal uncertainty. For most of the adult listeners and some of the children, the distracters produced higher thresholds (on average by 10 dB) and shallower psychometric function slopes. For most of the children, thresholds increased by 20 dB or more and psychometric functions were often nearly flat.

Adult↗

PubMed2002

Effects of positioning uncertainty and breathing on dose delivery and radiation pneumonitis prediction in breast cancer.

The quality of the radiation therapy delivered in the treatment of breast cancer is susceptible to setup errors and organ motion uncertainties. For 60 breast cancer patients (24 resected with negative node involvement, 13 resected with positive node involvement and 23 ablated) who were treated with three different irradiation techniques. these uncertainties are simulated. The delivered dose distributions in the lung were recalculated taking positioning uncertainty and breathing effects into account. In this way the real dose distributions delivered to the patients are more closely determined. The positioning uncertainties in the anteroposterior (AP) and the craniocaudal (CC) directions are approximated by Gaussian distributions based on the fact that setup errors are random. Breathing is assumed to have a linear behavior because of the chest wall movement during expiration and inspiration. The combined frequency distribution of the positioning and breathing distributions is obtained by convolution. By integrating the convolved distribution over a number of intervals, the positions and the weights of the fields that simulate the original 'effective fields' are calculated. Opposed tangential fields are simulated by a set of 5 pairs of fields in the AP direction and 3 such sets in the CC direction. Opposed AP + PA fields are simulated by a set of 3 pairs of fields in the AP direction and 3 such sets in the CC direction. Single frontal fields are simulated by a set of 5 fields. In radiotherapy for breast cancer, the lung is often partly within the irradiated volume even though it is a sensitive organ at risk. The influence of the deviation in the dose delivered by the original and the adjusted treatment plans on the clinical outcome is estimated by using the relative seriality model and the biologically effective uniform dose concept. Radiation pneumonitis is used as the clinical endpoint for lung complications. The adjusted treatment plans show larger lung complication probabilities than the original plans. This means that the true expected complications are often underestimated in clinical practice. The lung density variation during breathing is calculated from the maximal change in average density during tidal breathing. The change in density in the lung due to breathing is shown to have almost no influence on the dose distribution in the lung. The proposed treatment-plan adjustments taking positioning uncertainty and breathing effects into account indicate significant deviations in the dose delivery and the predicted lung complications.

Breast Neoplasms↗

PubMedDate not supplied

Aging and cognitive vigilance: effects of spatial uncertainty and event rate.

Age-related differences in cognitive vigilance were examined in a task requiring identification of a target (a lowercase letter) presented at three levels of spatial uncertainty (low, moderate, and high) and in the context of a low or high event rate. Thirty-six young (18-24 years) and 36 older (60-74 years) adults participated in 30-min vigilance sessions. Increased spatial uncertainty decreased target detection rate and d' to a greater extent in older adults than in young adults. No age differences were obtained for the low-spatial-uncertainty condition. The vigilance decrement--the decline in detection rate over time--was magnified when event rate was high and when spatial uncertainty was high. The results suggest that cognitive vigilance is age sensitive when demands on visual attention capacity are increased by high event rate or spatial uncertainty.

Adolescent↗

PubMed2002

Quantification of variability and uncertainty in lawn and garden equipment NOx and total hydrocarbon emission factors.

Variability refers to real differences in emissions among multiple emission sources at any given time or over time for any individual emission source. Variability in emissions can be attributed to variation in fuel or feedstock composition, ambient temperature, design, maintenance, or operation. Uncertainty refers to lack of knowledge regarding the true value of emissions. Sources of uncertainty include small sample sizes, bias or imprecision in measurements, nonrepresentativeness, or lack of data. Quantitative methods for characterizing both variability and uncertainty are demonstrated and applied to case studies of emission factors for lawn and garden (L&G) equipment engines. Variability was quantified using empirical and parametric distributions. Bootstrap simulation was used to characterize confidence intervals for the fitted distributions. The 95% confidence intervals for the mean grams per brake horsepower/hour (g/hp-hr) emission factors for two-stroke engine total hydrocarbon (THC) and NOx emissions were from -30 to +41% and from -45 to +75%, respectively. The confidence intervals for four-stroke engines were from -33 to +46% for THCs and from -27 to +35% for NOx. These quantitative measures of uncertainty convey information regarding the quality of the emission factors and serve as a basis for calculation of uncertainty in emission inventories (EIs).

Air Pollutants, Occupational↗

PubMed2004

Uncertainty requirements in radiative forcing of climate change.

The continuing increase in atmospheric carbon dioxide (CO2) makes it essential that climate sensitivity, the equilibrium change in global mean surface temperature that would result from a given radiative forcing, be quantified with known uncertainty. Present estimates are quite uncertain, 3 +/- 1.5 K for doubling of CO2. Model studies examining climate response to forcing by greenhouse gases and aerosols exhibit large differences in sensitivities and imposed aerosol forcings that raise questions regarding claims of their having reproduced observed large-scale changes in surface temperature over the 20th century. Present uncertainty in forcing, caused largely by uncertainty in forcing by aerosols, precludes meaningful model evaluation by comparison with observed global temperature change or empirical determination of climate sensitivity. Uncertainty in aerosol forcing must be reduced at least three-fold for uncertainty in climate sensitivity to be meaningfully reduced and bounded.

Aerosols↗

PubMedDate not supplied

Uncertainty management following a positive newborn screening for cystic fibrosis.

As advances are made in understanding the human genome, newborn screening for a variety of different diseases becomes more prevalent. Although this screening can provide a number of benefits, it also may be associated with various negative psychosocial consequences, including heightened uncertainty and anxiety about the child's health. Relying on videotaped interactions between health care providers and families whose child received a positive newborn screening test for cystic fibrosis (CF; N = 17), in this article we report on how the respective parties manage uncertainty. Although the goal of the providers appears to be one of reducing uncertainty, all parties to the interaction engage in behaviors that both manage and negotiate as opposed to just reduce uncertainty. Implications for theorizing about uncertainty management are discussed.

Adult↗

PubMed1997

Family members' uncertainty about parental chronic illness: the relationship of hemophilia and HIV infection to child functioning.

Examined the relationships among parental and child uncertainty about fathers' illnesses and child internalizing problems. Participants included 65 families in which the father had hemophilia, approximately one half of the fathers also were HIV infected. Within each family, respondents included the father, the mother and one child. Outcome variables included both self- and parent-reported child internalizing behaviors. Results indicated that family members' illness uncertainty was intercorrelated, that child uncertainty about the father's illness predicted both anxiety and depressive symptoms in the child, and that mother's uncertainty predicted child-reported anxiety beyond the child's uncertainty.

Adolescent↗

PubMed1997

Uncertainty and sensitivity analysis of the basic reproductive rate. Tuberculosis as an example.

The basic reproductive rate (R0) is a measure of the severity of an epidemic. On the basis of replicated Latin hypercube sampling, the authors performed an uncertainty and sensitivity analysis of the basic reproductive rate of tuberculosis (TB). The uncertainty analysis allowed for the derivation of a frequency distribution for R0 and the assessment of the relative contribution each of the three components of R0 made when TB epidemics first arose centuries ago. (The three components of R0 are associated with fast, slow, and relapse TB.) R0 estimates indicated the existence of fairly severe epidemics when TB epidemics first arose. The R0 for the susceptible persons who developed TB slowly (R0(slow)) contributed the most to the R0 estimates; however, the relative R0(slow) contribution decreased as the severity of TB epidemics increased. The sensitivity of the magnitude of R0 to the uncertainty in estimating values of each of the input parameters was assessed. These results indicated that five of the nine input parameters, because of their estimation uncertainty, were influential in determining the magnitude of R0. This uncertainty and sensitivity methodology provides results that can aid investigators in understanding the historical epidemiology of TB by quantifying the effect of the transmission processes involved. Additionally, this method can be applied to the R0 of any other infectious disease to estimate the probability of an epidemic outbreak.

Adult↗

PubMed2001

Uncertainty in particulate deposition for 1 microm AMAD particles in an adult lung model.

The ICRP 66 lung model may be used to determine dose estimates for members of the public via the inhalation pathway. A significant source of uncertainty in internal dosimetric modelling is due to particulate deposition in regions of the respiratory tract. Uncertainties in estimates of particulate deposition are present because model input parameters have their own inherent variability. These sources of uncertainty need to be examined in an effort to understand better model processes and to estimate better the doses received by individuals exposed through the inhalation pathway. An improved understanding of the uncertainty in particulate deposition will further guide research efforts and improve our ability to quantify internal dose estimates. The ICRP 66 lung deposition model is most sensitive to breathing rate when 1 microm AMAD particles are inhaled by members of the public. Uncertainties in deposition fractions are shown to span an order of magnitude with their distributions varying by gender for a particular lung region. The largest fractional deposition occurs in the deep lung alveolar and extrathoracic regions.

Administration, Inhalation↗

PubMed2002

Uncertainties on predicted concentrations of radionuclides in terrestrial foods and ingestion doses.

Models are routinely used to calculate doses following routine releases and potential accidental releases of radionuclides. These models contain a number of parameters. Values for many of these are not accurately known. The primary aim of this study was to determine the level of uncertainty on predicted concentrations of radionuclides in foods, and doses to individuals consuming those foods, arising from uncertainties on the model input parameter values. A secondary objective was to identify those input parameters whose uncertainty makes a major contribution to the overall uncertainty on the predicted endpoints. The methodology adopted and results obtained are presented for the following radionuclides: 90Sr, 131I, 137Cs and 239Pu. The estimated uncertainty ratios (the ratio of the 95th to the 5th percentile) are frequently very large, often two to three orders of magnitude. The results of this study may be used to identify areas where further research could improve assessment capabilities.

Accidents↗

PubMed1999

Adults' experience with asthma and their reported uncertainty and coping strategies.

This study examined the uncertainty experienced by persons with asthma and the coping strategies they used. The sample of 99 adults was interviewed by the investigators. Subjects responded to demographic and illness-related questions and completed the Mishel Uncertainty in Illness Scale and the Jalowiec Coping Scale. Subjects who had asthma for a longer duration reported lower levels of uncertainty. Those who were hospitalized because of asthma and those for whom pollen was a trigger experienced greater uncertainty. Females, individuals who went to an emergency department because of asthma, and those who attended pulmonary support groups used more coping strategies. Understanding the sources of perceived uncertainty may assist individuals to cope with and manage the chronic and acute phases of asthma.

Adaptation, Psychological↗

PubMed2001

Preliminary uncertainty analysis for the doses estimated using the Techa River dosimetry system--2000.

The Mayak Production Association (MPA) was the first facility in the former Soviet Union for the production of plutonium. As a result of failures in the technological processes in the late 1940's and early 1950's, members of the public were exposed via discharge of about 10(17) Bq of liquid wastes into the Techa River (1949-1956). Residents of many villages downstream on the Techa River were exposed via a variety of pathways; the more significant included drinking of water from the river and external gamma exposure due to proximity to sediments and shoreline. The specific aim of this project is to enhance the reconstruction of external and internal radiation doses for individuals in the Extended Techa River Cohort. The purpose of this paper is to present the approaches being used to evaluate the uncertainty in the calculated individual doses and to provide example and representative results of the uncertainty analyses. The magnitude of the uncertainties varies depending on location and time of individual exposure, but the results from reference-individual calculations indicate that for external doses, the range of uncertainty is about a factor of four to five. For internal doses, the range of uncertainty depends on village of residence, which is actually a surrogate for source of drinking water. For villages with single sources of drinking water (river or well), the ratio of the 97.5th percentile-to 2.5th percentile estimates can be a factor of 20 to 30. For villages with mixed sources of drinking water (river and well), the ratio of the range can be over two orders of magnitude.

Databases, Factual↗

PubMed2002

Age-specific uncertainty in particulate deposition for 1 microm AMAD particles using the ICRP 66 lung model.

The ICRP 66 lung model may be used to determine age-specific dose estimates for members of the public via the inhalation pathway. A significant source of uncertainty in internal dosimetric modeling is due to particulate deposition in regions of the respiratory tract. Uncertainties in estimates of particulate deposition are present because of the inherent variability in the deposition model and its various input parameters. An improved understanding of the uncertainty in particulate deposition will further guide research efforts and improve our ability to quantify internal dose estimates. The ICRP 66 lung deposition model is most sensitive to breathing rate when 1 microm AMAD particles are inhaled by members of the public. Uncertainties in deposition fractions are shown to span an order of magnitude with their distributions varying by age and sex for a particular lung region. Age-specific uncertainties of deposition fraction demonstrate increased estimates of extrathoracic deposition in younger age groups due to the decreased size of the respiratory tract airways. This age-specific trend becomes more pronounced for very young children and infants. The largest fractional deposition occurs in the alveolar and extrathoracic regions, regardless of age and sex.

Adolescent↗

PubMed2003

Influences of parameter uncertainties within the ICRP-66 respiratory tract model: regional tissue doses for 239PuO2 and 238UO2/238U3O8.

This paper extends an examination of the influence of parameter uncertainties on regional doses to respiratory tract tissues for short-ranged alpha particles using the ICRP-66 respiratory tract model. Previous papers examined uncertainties in the deposition and clearance aspects of the model. The critical parameters examined in this study included target tissue depths, thicknesses, and masses, particularly within the thoracic or lung regions of the respiratory tract. Probability density functions were assigned for the parameters based on published data. The probabilistic computer code LUDUC (Lung Dose Uncertainty Code) was used to assess regional and total lung doses from inhaled aerosols of 239PuO2 and 238UO2/238U3O8. Dose uncertainty was noted to depend on the particle aerodynamic diameter. Additionally, dose distributions were found to follow a lognormal distribution pattern. For 239PuO2 and 238UO2/238U3O8, this study showed that the uncertainty in lung dose increases by factors of approximately 50 and approximately 70 for plutonium and uranium oxides, respectively, over the particle size range from 0.1 to 20 microm. For typical exposure scenarios involving both radionuclides, the ratio of the 95% dose fractile to the 5% dose fractile ranged from approximately 8-10 (corresponding to a geometric standard deviation, or GSD, of about 1.7-2) for particle diameters of 0.1 to 1 microm. This ratio increased to about 370 for plutonium oxide (GSD approximately 4.5) and to about 600 for uranium oxide (GSD approximately 5) as the particle diameter approached 20 microm. However, thoracic tissue doses were quite low at larger particle sizes because most of the deposition occurred in the extrathoracic airways. For 239PuO2, median doses from LUDUC were found be in general agreement with those for Reference Man (via deterministic LUDEP 2.0 calculations) in the particle range of 0.1 to 5 microm. However, median doses to the basal cell nuclei of the bronchial airways (BB(bas)) calculated by LUDUC were found to be approximately 6 times higher than LUDEP reference doses. The higher BB(bas) doses were directly attributed to discrepancies between the ICRP default thickness for the bronchial epithelium (55 microm) and the probability density function assumed within LUDUC (uniform distribution from 20 to 60 microm based upon detailed literature reviews).

Adolescent↗

PubMed2005

Uncertainty of data, fuzzy membership functions, and multilayer perceptrons.

Probability that a crisp logical rule applied to imprecise input data is true may be computed using fuzzy membership function (MF). All reasonable assumptions about input uncertainty distributions lead to MFs of sigmoidal shape. Convolution of several inputs with uniform uncertainty leads to bell-shaped Gaussian-like uncertainty functions. Relations between input uncertainties and fuzzy rules are systematically explored and several new types of MFs discovered. Multilayered perceptron (MLP) networks are shown to be a particular implementation of hierarchical sets of fuzzy threshold logic rules based on sigmoidal MFs. They are equivalent to crisp logical networks applied to input data with uncertainty. Leaving fuzziness on the input side makes the networks or the rule systems easier to understand. Practical applications of these ideas are presented for analysis of questionnaire data and gene expression data.

Algorithms↗

PubMed2003

Probabilistic framework for the estimation of the adult and child toxicokinetic intraspecies uncertainty factors.

Human health risk assessments use point values to develop risk estimates and thus impart a deterministic character to risk, which, by definition, is a probability phenomenon. The risk estimates are calculated based on individuals and then, using uncertainty factors (UFs), are extrapolated to the population that is characterized by variability. Regulatory agencies have recommended the quantification of the impact of variability in risk assessments through the application of probabilistic methods. In the present study, a framework that deals with the quantitative analysis of uncertainty (U) and variability (V) in target tissue dose in the population was developed by applying probabilistic analysis to physiologically-based toxicokinetic models. The mechanistic parameters that determine kinetics were described with probability density functions (PDFs). Since each PDF depicts the frequency of occurrence of all expected values of each parameter in the population, the combined effects of multiple sources of U/V were accounted for in the estimated distribution of tissue dose in the population, and a unified (adult and child) intraspecies toxicokinetic uncertainty factor UFH-TK was determined. The results show that the proposed framework accounts effectively for U/V in population toxicokinetics. The ratio of the 95th percentile to the 50th percentile of the annual average concentration of the chemical at the target tissue organ (i.e., the UFH-TK) varies with age. The ratio is equivalent to a unified intraspecies toxicokinetic UF, and it is one of the UFs by which the NOAEL can be divided to obtain the RfC/RfD. The 10-fold intraspecies UF is intended to account for uncertainty and variability in toxicokinetics (3.2x) and toxicodynamics (3.2x). This article deals exclusively with toxicokinetic component of UF. The framework provides an alternative to the default methodology and is advantageous in that the evaluation of toxicokinetic variability is based on the distribution of the effective target tissue dose, rather than applied dose. It allows for the replacement of the default adult and children intraspecies UF with toxicokinetic data-derived values and provides accurate chemical-specific estimates for their magnitude. It shows that proper application of probability and toxicokinetic theories can reduce uncertainties when establishing exposure limits for specific compounds and provide better assurance that established limits are adequately protective. It contributes to the development of a probabilistic noncancer risk assessment framework and will ultimately lead to the unification of cancer and noncancer risk assessment methodologies.

Adolescent↗

PubMed1987

Sensitivity and uncertainty studies of the CRAC2 computer code.

We have studied the sensitivity of health impacts from nuclear reactor accidents, as predicted by the CRAC2 computer code, to the following sources of uncertainty: (1) the model for plume rise, (2) the model for wet deposition, (3) the meteorological bin-sampling procedure for selecting weather sequences with rain, (4) the dose conversion factors for inhalation as affected by uncertainties in the particle size of the carrier aerosol and the clearance rates of radionuclides from the respiratory tract, (5) the weathering half-time for external ground-surface exposure, and (6) the transfer coefficients for terrestrial foodchain pathways. Predicted health impacts usually showed little sensitivity to use of an alternative plume-rise model or a modified rain-bin structure in bin-sampling. Health impacts often were quite sensitive to use of an alternative wet-deposition model in single-trial runs with rain during plume passage, but were less sensitive to the model in bin-sampling runs. Uncertainties in the inhalation dose conversion factors had important effects on early injuries in single-trial runs. Latent cancer fatalities were moderately sensitive to uncertainties in the weathering half-time for ground-surface exposure, but showed little sensitivity to the transfer coefficients for terrestrial foodchain pathways. Sensitivities of CRAC2 predictions to uncertainties in the models and parameters also depended on the magnitude of the source term, and some of the effects on early health effects were comparable to those that were due only to selection of different sets of weather sequences in bin-sampling.

Accidents↗