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Results for “Uncertainty”

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At least 325 records · Page 18Linked to original sources

PubMed2002

Estimation of the total uncertainty of sky-radiance measurements in field experimental conditions: implications for the aerosol single-scattering albedo.

We compare the spectral sky radiance measured by three ground-based optical radiometers during the second Aerosol Characterization Experiment (ACE-2) to estimate the total uncertainty of the radiance in field experimental conditions. The propagation of this uncertainty on the column-integrated aerosol single-scattering albedo omega0 at 868 nm is investigated. The radiance measurements are affected by a systematic gain uncertainty of less than 2% in the visible spectral region and within 6% in the near-IR region. Correcting the measured radiance by a systematic uncertainty reduces the dispersion of the omega0 from 0.07 to 0.03. Besides, the total relative uncertainty of the radiance measurements in field experimental conditions is within 4% at any wavelength. The corresponding uncertainty delta omega0 is 4% for an aerosol optical thickness of 0.2.

Journal Article↗

PubMed2001

Effect of inherent location uncertainty on detection of stationary targets in noisy image sequences.

The effect of inherent location uncertainty on the detection of stationary targets was determined in noisy image sequences. Targets were thick and thin projected cylinders mimicking arteries, catheters, and guide wires in medical imaging x-ray fluoroscopy. With the use of an adaptive forced-choice method, detection contrast sensitivity (the inverse of contrast) was measured both with and without marker cues that directed the attention of observers to the target location. With the probability correct clamped at 80%, contrast sensitivity increased an average of 77% when the marker was added to the thin-cylinder target. There was an insignificant effect on the thick cylinder. The large enhancement with the thin cylinder was obtained even though the target was located exactly in the center of a small panel, giving observers the impression that it was well localized. Psychometric functions consisting of d' plotted as a function of the square root of the signal-energy-to-noise-ratio gave a positive x intercept for the case of the thin cylinder without a marker. This x intercept, characteristic of uncertainty in other types of detection experiments, disappeared when the marker was added or when the thick cylinder was used. Inherent location uncertainty was further characterized by using four different markers with varying proximity to the target. Visual detection by human observers increased monotonically as the markers better localized the target. Human performance was modeled as a matched-filter detector with an uncertainty in the placement of the template. The removal of a location cue was modeled by introducing a location uncertainty of approximately equals 0.4 mm on the display device or only 7 microm on the retina, a size on the order of a single photoreceptor field. We conclude that detection is affected by target location uncertainty on the order of cellular dimensions, an observation with important implications for detection mechanisms in humans. In medical imaging, the results argue strongly for inclusion of high-contrast visualization markers on catheters and other interventional devices.

Artifacts↗

PubMed2001

Space radiation cancer risks and uncertainties for Mars missions.

Projecting cancer risks from exposure to space radiation is highly uncertain because of the absence of data for humans and because of the limited radiobiology data available for estimating late effects from the high-energy and charge (HZE) ions present in the galactic cosmic rays (GCR). Cancer risk projections involve many biological and physical factors, each of which has a differential range of uncertainty due to the lack of data and knowledge. We discuss an uncertainty assessment within the linear-additivity model using the approach of Monte Carlo sampling from subjective error distributions that represent the lack of knowledge in each factor to quantify the overall uncertainty in risk projections. Calculations are performed using the space radiation environment and transport codes for several Mars mission scenarios. This approach leads to estimates of the uncertainties in cancer risk projections of 400-600% for a Mars mission. The uncertainties in the quality factors are dominant. Using safety standards developed for low-Earth orbit, long-term space missions (>90 days) outside the Earth's magnetic field are currently unacceptable if the confidence levels in risk projections are considered. Because GCR exposures involve multiple particle or delta-ray tracks per cellular array, our results suggest that the shape of the dose response at low dose rates may be an additional uncertainty for estimating space radiation risks.

Cosmic Radiation↗

PubMed2004

A reanalysis of thyroid neoplasms in the Israeli tinea capitis study accounting for dose uncertainties.

In the 1940s and 1950s, children in Israel were treated for tinea capitis by irradiation to the scalp to induce epilation. Follow-up studies of these patients and of other radiation- exposed populations show an increased risk of malignant and benign thyroid tumors. Those analyses, however, assume that thyroid dose for individuals is estimated precisely without error. Failure to account for uncertainties in dosimetry may affect standard errors and bias dose-response estimates. For the Israeli tinea capitis study, we discuss sources of uncertainties and adjust dosimetry for uncertainties in the prediction of true dose from X-ray treatment parameters. We also account for missing ages at exposure for patients with multiple X-ray treatments, since only ages at first treatment are known, and for missing data on treatment center, which investigators use to define exposure. Our reanalysis of the dose response for thyroid cancer and benign thyroid tumors indicates that uncertainties in dosimetry have minimal effects on dose-response estimation and for inference on the modifying effects of age at first exposure, time since exposure, and other factors. Since the components of the dose uncertainties we describe are likely to be present in other epidemiological studies of patients treated with radiation, our analysis may provide a model for considering the potential role of these uncertainties.

Adolescent↗

PubMedDate not supplied

Uncertainty and sensitivity analysis of spatial predictions of heavy metals in wheat.

Heavy metals seriously threaten the health of human beings when they enter the food chain. Therefore, policymakers require precise predictions of heavy metal concentrations in agricultural crops. In this paper we quantify the uncertainty of regression predictions of Cd and Pb in wheat (Triticum aestivum L.) and the contributions to the uncertainties in these predictions associated with inputs to the regression model. For each node of the 500- x 500-m grid covering the arable soils in The Netherlands, a latin hypercube sample size of 1000 is constructed from the uncertainty distributions of the explanatory variables (pH, soil organic matter [SOM], and heavy metal concentration in soil), the regression coefficients, and the random term of the regression model. This sample is used as input for the regression model to obtain 1000 values from the uncertainty distributions of the log(Cd) and log(Pb) concentration in wheat. There were no nodes where the recent EU quality standards for Cd and Pb (0.2 mg kg(-1) fresh wt.) in wheat were almost certain to be exceeded. For most nodes with clay soils, the quality standard for Cd in wheat almost certainly will not be exceeded; for Pb this is much less certain. The uncertainty in the Cd concentration in soil contributes most to the uncertainty in the predicted Cd concentrations in wheat (36% on the average), followed by the random term of the regression model (23%). For Pb the contribution of the random term is by far the largest (52%).

Agriculture↗

PubMed2006

Directional uncertainty in visually guided pointing.

Studies of the relationship between stimulus-response uncertainty and reaction times indicate three qualitatively different functions: Hick's law, simple-choice step function, or flat curve (no effect at all). The extent of stimulus-response S-R) compatibility appears to interact with the effects of uncertainty on response times. One possible hypothesis regarding these various S-R uncertainty functions is that uncertainty will have an effect whenever the stimuli and their associated responses are not within the same egocentric spatial coordinates. We tested this hypothesis in 5 undergraduate participants (2 men, M age 18.7 yr., range 18-20) by investigating the time-course of pointing to peripherally located visual targets under four different levels of uncertainty (1, 2, 4, or 8 possible locations). Surprisingly, the resulting response function does not match any of those previously reported. Visually guided pointing produced a quadratic reaction time function as S-R uncertainty increases in log2 steps from 1 to 8.

Adolescent↗

PubMedDate not supplied

Uncertainty, spiritual well-being, and psychosocial adjustment to chronic illness.

This research was undertaken to assess spiritual well-being as an internal coping resource to buffer the effects of uncertainty on psychosocial adjustment among 94 persons with diabetes mellitus. Five instruments were used to collect data; descriptive, correlational, multivariate, and content analysis procedures were used for data analysis. A predicted negative relationship between uncertainty and spiritual well-being was supported, with a stronger relationship between the existential well-being component of spiritual well-being and uncertainty than the religious well-being component. Uncertainty explained 43% of the variance in psychosocial well-being; existential well-being added an additional 10%, suggesting that it serves as a buffer between uncertainty and psychosocial well-being. The findings suggest that spiritual well-being may be an important internal resource for persons forced to adjust to uncertainty related to long-term health problems such as diabetes mellitus.

Adaptation, Psychological↗

PubMed1988

[Discrepancy in the scores of uncertainty perceived by patients and nurses' interperson perception].

The purpose of this study was to assess and compare discrepancy in the scores of uncertainty perceived by patients and nurses' interperson perception. For this study, 124 hospitalized patients and the same numbered nurses assigned for direct care of each 124 patients were selected from general ward of C. University Hospital in Seoul during the time period from September to November 1987. Degree of uncertainty was measured by 27 items modified from Mishel Uncertainty in Illness Scale (M-UIS), and was utilized by a Likert type scale The data were analysed by Mcnemar-test, Unpaired t-test, ANOVA, Scheffé-test and Stepwise multiple regression. The results are summarized as follows: 1. The discrepancy in the scores of uncertainty perceived by patients and nurses' interperson perception showed significant differences in 23 of 27 items: 11 of 23 items showed that the scores of patients' perception of uncertainty were higher than that of nurses' interperson perception of uncertainty. but 12 of 23 items were revealed reversely. 2. With regard to nurse's demographic variables, the discrepancy scores were the highest in the group under 22 years of age (F = 3.20, p = .026) and in the group less than 1 year of nursing experience among 4 groups (F = 4.41, p = .006). 3. The discrepancy scores had a tendency to be lowered in the higher age group (r = .27, p = .0026) and in the longer experienced group (r = .25, p = .0052).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed2026

Characterizing the Uncertainty, Misclassification and Inconsistency of Polygenic Prediction.

Polygenic risk scores (PRSs) hold promise for precision medicine, yet their clinical translation is hindered by substantial uncertainty in individual risk estimates and often limited agreement in risk stratification across multiple PRSs for the same disease. We develop a unified inferential framework to calibrate PRS point estimates and uncertainties for both quantitative traits and binary phenotypes, and to characterize how PRS accuracy, uncertainty, pairwise correlation jointly determine misclassification and classification inconsistency. We show, both theoretically and empirically, that individual- and population-level misclassification and inconsistency rates are highly predictable in independent datasets. We further evaluate PRS integration and uncertainty-aware probabilistic thresholding strategies that reduce misclassification and improve concordance in risk stratification. Together, these results demonstrate that instability in PRS-based classification is a predictable statistical consequence of uncertainty and establish a principled foundation for incorporating uncertainty into PRS-based risk interpretation, communication, and clinical decision-making.

Journal Article↗

PubMed2000

Uncertainty in childhood illness: a synthesis of the parent and child literature.

Uncertainty has increasingly been identified as an important construct in the clinical and empirical literature on families' responses to serious childhood illnesses. Most of the work has focused on parents' perceptions of uncertainty, but several recent studies have demonstrated that children are also affected by uncertainties inherent in the illness experience. Findings from 44 reports of parental uncertainty and 12 reports of children's uncertainty were reviewed to determine what is currently known about uncertainty in the context of acute and chronic childhood illness. Pertinent conceptual and methodological issues are identified and directions for future research are suggested.

Acute Disease↗

PubMed2001

Evidence-based medicine, clinical uncertainty, and learning to doctor.

For the past two decades, evidence-based medicine (EBM), or the reliance on current scientific evidence to reach medical decisions, has been embraced as a new paradigm to standardize clinical care. Drawing from in-depth interviews with seventeen pediatric residents in two residency programs, we evaluate the extent to which the medical sociology scholarship on uncertainty analytically elucidates the recent influx of EBM during residency training. Our findings suggest that residents interpret EBM in varying ways to match their work practices: "Librarians" consult the literature while "researchers" evaluate it critically. For both groups, EBM might generate new uncertainties due to the increased reliance on information technologies and epidemiology. Whether EBM reduces uncertainty depends upon the residents' understanding of standardized knowledge and consequent incorporation of EBM in their clinical practice. Contrary to the predictions of some sociologists, EBM does not lead to a diminishment of humanitarian values in medical care. Nor does EBM lead to a science-based meritocracy on the patient ward, as claimed by some EBM advocates. Our conceptual updating of uncertainty emphasizes the continuous management of uncertainty during the medical socialization process. We argue that managing uncertainty develops along with what we term evidence-based clinical judgment.

Clinical Competence↗

PubMed1988

Dealing with uncertainty: statistics for an aging population.

"Uncertainty in statistics and demographic projections for aging and other policy purposes comes from four sources: differences in definitions, sampling error, nonsampling error, and scientific uncertainty. Some of these uncertainties can be reduced by proper planning and coordination, but most often decisions have to be made in the face of some remaining uncertainty. Although decision makers have a tendency to ignore uncertainty, doing so does not lead to good policy-making. Techniques for estimating and reporting on uncertainty include sampling theory, assessment of experts' subjective distributions, sensitivity analysis, and multiple independent estimates." The primary geographical focus is on the United States.

Americas↗

PubMed2005

Uncertainty in predicting riverbed erosion caused by urban stormwater discharge.

Ecologically based criteria require an integrated modeling approach. Due to the complexity of the system, the stochastic nature of loads, and the model abstractions, many uncertainties are involved. In this study, a simple integrated model is applied, which Swiss engineers employ to assess the impact of urban stormwater discharges on riverbed stability. In the course of a case study, an uncertainty analysis is carried out focusing on parameter uncertainties. The underlying context of the uncertainties is evaluated, and a variance-based sensitivity analysis is presented estimating the local uncertainty contribution of each parameter. The results reveal that the largest contributions stem from the model components describing the natural system. An experimental design is proposed that manages to reduce the output uncertainty significantly. Finally, we discuss the benefits of following the proposed procedure.

Cities↗

PubMedDate not supplied

Uncertainty in gynecological cancer: a test of the mediating functions of mastery and coping.

The purpose of this study was to test a portion of the uncertainty in illness model to determine whether mastery would be strengthened or weakened under conditions of uncertainty, and to test the ability of mastery and coping to function as mediators in the model. Mastery was proposed to mediate the relationship between uncertainty and the appraisal of danger and opportunity. Coping was proposed to mediate the relationships between danger or opportunity and emotional distress. Data were collected on a sample of 131 women receiving treatment for gynecological cancer. Findings support mastery as weakened under conditions of uncertainty and functioning as a situationally specific personality factor. Mastery was a significant mediator of the relationship between uncertainty and the appraisal of danger and opportunity; although the mediation effect for the relationship between uncertainty and danger was stronger. While two coping strategies were found to function as significant mediators between danger or opportunity and emotional distress, the mediation effect was very small.

Adaptation, Psychological↗

PubMed1998

Statistically accurate estimation of hormone concentrations and associated uncertainties: methodology, validation, and applications.

We describe a data reduction procedure to assign statistically accurate estimates of unknown hormone concentrations, with associated uncertainties, based on experimental uncertainties in sample replicates and the fitted calibration curve. Three mathematical calibration curve functions are considered. The one providing optimal statistical characterization of reference calibrators is chosen for unknown evaluation. Experimental error is addressed by assigning and propagating uncertainty estimates for each measured response (including zero-dose responses) by an empirically determined discrete uncertainty profile and by propagating calibration curve uncertainty. Discrete uncertainty profiles account for both response precision (replicability) and accuracy (deviation from predicted calibration curves) without relying on assumed theoretical response variance-assay response relations. The validity of assigning variable response weighting by this procedure was assessed by Monte Carlo simulations based on chemiluminescence growth hormone calibration curves. Much-improved accuracy and estimated precision are achieved for unknown hormone concentrations, particularly extremely low concentrations, by using this variable response weighting procedure.

Data Interpretation, Statistical↗

PubMed2006

Testing a model of symptoms, communication, uncertainty, and well-being, in older breast cancer survivors.

Among older, long-term breast cancer survivors, symptoms from previous treatment can generate uncertainty about whether they represent co-morbid conditions, recurrence, or normal aging. This uncertainty can result in emotional distress and thoughts of recurrence. Communication with health care providers may help women reduce uncertainty and improve both emotional and cognitive well-being. To assess the influence of symptoms, uncertainty, and communication with providers on well-being, data from 203 Caucasian and African American survivors, 5-9 years post treatment, were tested using structural equation modeling. Symptoms, age, and uncertainty had the strongest influence on well-being, regardless of race. There was an unexpected positive association between patient-provider communication and thoughts of recurrence. Descriptive analysis revealed that 52% of women were unable to achieve their desired decision-making role with health care providers.

Affect↗

PubMed2005

A standard approach to measurement uncertainties for scientists and engineers in medicine.

The critical nature of health care demands high performance levels from medical equipment. To ensure these performance levels are maintained, medical physicists and biomedical engineers conduct a range of measurements on equipment during acceptance testing and on-going quality assurance programs. Wherever there are measurements, there are measurement uncertainties with potential conflicts between the measurements made by installers, owners and occasionally regulators. Prior to 1993, various methods were used to calculate and report measurement uncertainties. In 1993, the International Organization for Standardization published the Guide to the Expression of Uncertainty in Measurement (GUM). The document was jointly published with six international organizations principally involved in measurements and standards. The GUM is regarded as an international benchmark on how measurement uncertainty should be calculated and reported. Despite the critical nature of these measurements, there has not been widespread use of the GUM by medical physicists and biomedical engineers. This may be due to the complexity of the GUM. Some organisations have published guidance on the GUM tailored to specific measurement disciplines. This paper presents the philosophy behind the GUM, and demonstrates, with a medical physics measurement example, how the GUM recommends uncertainties be calculated and reported.

Algorithms↗

PubMed2005

Uncertainty assessment of VOC emissions from paint in The Netherlands using the NUSAP system.

We demonstrate an innovative approach to uncertainty assessment known as the NUSAP system, to assess qualitative and quantitative uncertainty for the case of emissions of volatile organic compounds (VOC) from paint in The Netherlands. Using expert elicitation, we identified key sources of error, critical assumptions, and bias in the monitoring process. We assessed pedigree and probabilistic uncertainty of all input quantities. We used four pedigree criteria to assess the strength of the knowledge base: proxy representation, empirical basis, methodological rigour and degree of validation. Using Monte Carlo analysis, we assessed sensitivity and propagation of uncertainty. Results for sensitivity and pedigree were combined in a 'NUSAP Diagnostic Diagram', which effectively highlighted the assumption for VOC percentage of imported paint as the weakest spot in the monitoring of VOC emissions. We conclude that NUSAP facilitates systematic scrutinization of method and underlying assumptions and structures creative thinking on sources of error and bias. It provides a means to prioritise uncertainties and focus research efforts on the potentially most problematic parameters and assumptions, at the same time identifying specific weaknesses in the knowledge base. With NUSAP, nuances of meaning about quantities can be conveyed concisely and clearly, to a degree that is not possible with statistic methods only.

Air Pollutants↗