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PubMed2005

Using the W&H integrated uncertainty analysis framework with non-initiated experts.

The W&H (Walker and Harremoës) integrated uncertainty analysis framework was put forward with the aim of providing a conceptual basis for the systematic treatment of uncertainty in model-based decision support activities such as policy analysis, integrated assessment and risk assessment. It provides a heuristic tool that can be applied in decision support exercises to classify and report the various dimensions of uncertainty. The intention is to stimulate better communication among analysts as well as between them and policymakers and stakeholders. The framework successfully articulates diverse scholarly understandings of 'uncertainty', 'ignorance', and 'quality' in science for policy, Nevertheless, experience with the W&H framework has revealed that many of the concepts put forward are relatively unfamiliar--and perhaps somewhat controversial--to experts practising decision support. Thus, efforts are required to communicate the W&H framework to experts in such a way that their knowledge of uncertainty is elicited adequately, without them being overly intimidated or confused by the novelty of the concepts presented to them. After introducing the W&H conceptual framework, this paper presents the methodology that was used in applying the W&H framework in expert elicitations on uncertainty in the risk assessment of genetically modified crops. Experiences with the use of this methodology are discussed and recommendations for further improvement are given.

Decision Support Techniques↗

PubMed1984

Genetic counseling and reproductive uncertainty.

Of 836 fertile women seeking genetic counseling, 544 (65%) reported that their major reason for doing so was to obtain information to help in deciding if they should have a child. Thirty-four percent of these 836 women entered counseling uncertain about undertaking a pregnancy in the next 2 years. After counseling, 28% of the 836 had uncertain pregnancy intentions. These included 66% of those who were uncertain and 11% of those who were reproductively certain before counseling. Stepwise logistic regression identified the following as independently and significantly associated with reproductive uncertainty after counseling: 1) uncertainty before counseling; 2) uncertainty about ideal family size; 3) concern about the effects of an affected child on the client's social life; 4) perceived serious problems caring for a child with a birth defect now living at home; and 5) new concerns raised in counseling. Reproductive uncertainty after counseling was not related to characteristics of the risked birth defect, level of risk, treatment potential, or client learning of medical and genetic facts. These data suggest that genetic counseling will not eliminate reproductive uncertainty for many clients, because this uncertainty is related to factors mainly outside the usual scope of counseling.

Adolescent↗

PubMed2000

Reducing uncertainty of risk estimates for mixtures of chemicals within regulatory constraints.

Reducing uncertainty in estimated risks is always desirable. While regulatory assumptions and policies regarding risk assessment of chemicals can be debated, these are the rules under which many risk assessments are currently conducted. Methods for reducing the uncertainty in risk estimates generated under those rules are therefore useful, whether or not one agrees with the models and the underlying assumptions that comprise those rules. The guidance for risk assessment of mixtures of chemicals used by EPA was reexamined to determine methods for reducing the uncertainty in the cumulative risk estimates. It was found that the uncertainty could be significantly reduced if the assumptions concerning the assessment of mixtures of chemicals were combined with the assumptions for evaluating the risks of individual chemicals. Methods are proposed for reducing the uncertainty of mixtures of chemicals whose individual constituents are evaluated by cancer potency factors, hazard quotients, or margins of exposure. The methods developed do not require data beyond that which would be required for generating the current risk estimates for the individual chemicals. These analyses also demonstrated that some of the assumptions currently in use for regulatory risk assessment may lead to inconsistencies that should be reevaluated. As the proposed methods do not require any change in the current assumptions to reduce uncertainty in the risk estimates, the proposed methods should prove useful until such time as the assumptions are reevaluated and possibly changed.

Animals↗

PubMed2003

Evaluation of the combined measurement uncertainty in isotope dilution by MC-ICP-MS.

The combination of metrological weighing, the measurement of isotope amount ratios by a multicollector inductively coupled plasma mass spectrometer (MC-ICP-MS) and the use of high-purity reference materials are the cornerstones to achieve improved results for the amount content of lead in wine by the reversed isotope dilution technique. Isotope dilution mass spectrometry (IDMS) and reversed IDMS have the potential to be a so-called primary method, with which close comparability and well-stated combined measurement uncertainties can be obtained. This work describes the detailed uncertainty budget determination using the ISO-GUM approach. The traces of lead in wine were separated from the matrix by ion exchange chromatography after HNO(3)/H(2)O(2) microwave digestion. The thallium isotope amount ratio ( n((205)Tl)/ n((203)Tl)) was used to correct for mass discrimination using an exponential model approach. The corrected lead isotope amount ratio n((206)Pb)/ n((208)Pb) for the isotopic standard SRM 981 measured in our laboratory was compared with ratio values considered to be the least uncertain. The result has been compared in a so-called pilot study "lead in wine" organised by the CCQM (Comité Consultatif pour la Quantité de Matière, BIPM, Paris; the highest measurement authority for analytical chemical measurements). The result for the lead amount content k(Pb) and the corresponding expanded uncertainty U given by our laboratory was:k(Pb)=1.329 x 10-10mol g-1 (amount content of lead in wine)U[k(Pb)]=1.0 x 10-12mol g-1 (expanded uncertainty U=kxuc, k=2)The uncertainty of the main influence parameter of the combined measurement uncertainty was determined to be the isotope amount ratio R(206,B) of the blend between the enriched spike and the sample.

Lead↗

PubMed2001

Identifying influences on model uncertainty: an application using a forest carbon budget model.

Uncertainty is an important consideration for both developers and users of environmental simulation models. Establishing quantitative estimates of uncertainty for deterministic models can be difficult when the underlying bases for such information are scarce. We demonstrate an application of probabilistic uncertainty analysis that provides for refinements in quantifying input uncertainty even with little information. Uncertainties in forest carbon budget projections were examined with Monte Carlo analyses of the model FORCARB. We identified model sensitivity to range, shape, and covariability among model probability density functions, even under conditions of limited initial information. Distributional forms of probabilities were not as important as covariability or ranges of values. Covariability among FORCARB model parameters emerged as a very influential component of uncertainty, especially for estimates of average annual carbon flux.

Carbon↗

PubMed1995

Methods for displaying macromolecular structural uncertainty: application to the globins.

Most molecular graphics programs ignore any uncertainty in the atomic coordinates being displayed. Structures are displayed in terms of perfect points, spheres, and lines with no uncertainty. However, all experimental methods for defining structures, and many methods for predicting and comparing structures, associate uncertainties with each atomic coordinate. We have developed graphical representations that highlight these uncertainties. These representations are encapsulated in a new interactive display program, PROTEAND. PROTEAND represents structural uncertainty in three ways: (1) The traditional way: The program shows a collection of structures as superposed and overlapped stick-figure models. (2) Ellipsoids: At each atom position, the program shows an ellipsoid derived from a three-dimensional Gaussian model of uncertainty. This probabilistic model provides additional information about the relationship between atoms that can be displayed as a correlation matrix. (3) Rigid-body volumes: Using clouds of dots, the program can show the range of rigid-body motion of selected substructures, such as individual alpha helices. We illustrate the utility of these display modalities by the applying PROTEAND to the globin family of proteins, and show that certain types of structural variation are best illustrated with different methods of display.

Animals↗

PubMed1990

Uncertainties in dosimetric data and beam calibration.

Recent studies indicate that the calibration of therapeutic beams is one of the main sources of uncertainty in the mean absorbed dose to the target volume in radiotherapy. Interaction coefficients and data used through the different steps in the calibration are pointed out as the main contribution to this uncertainty. Procedures used to select dosimetric data, that is, input parameters used in the specification of the quality of the beam, cause another contribution. In this paper the actual status of the data used for the dosimetry of photon and electron beams is introduced first. Uncertainties along the dosimetric chain are analyzed according to the procedure and data used in recent publications. Uncertainties in stopping-power ratios, considered the main contribution, are discussed in detail starting from the basic electron stopping-power data. Overall uncertainties in the presently available set of stopping-power ratios are analyzed. Recent developments in the dosimetry of electron beams, related to the effect of energy and angular spread and electron and photon contamination, are discussed in connection with the procedure to select stopping-power ratios for clinical dosimetry. Uncertainties along the dosimetric chain are evaluated in terms of the present knowledge of error sources.

Calibration↗

PubMedDate not supplied

Systematic and non-systematic effects of the uncertainty of the sample position in gamma-ray spectrometry.

When cylindrical samples placed coaxially with the detector are measured on a gamma-ray spectrometer, the position of the sample very often deviates from an ideal one with the axes of the sample and the detector less than perfectly aligned. If a calibrated source is used prior to the measurement and is presumed to have been positioned correctly, one might conclude that the misalignment of the measured sample should result in an uncertainty of the reported nuclide activity, since the efficiencies of the sample and the calibrated source are effectively different due to the difference in placement. The efficiency of a displaced cylindrical sample, however, is always lower than the one of a sample that is perfectly aligned. The net effect of misalignment can therefore be not only an increase in the uncertainty of the activity, but also a systematic error in its evaluation. Since the Guide to the Expression of Uncertainty in Measurement requires that all such systematic effects be corrected for, we have developed a method to assess the change in the efficiency resulting from misalignment and to introduce the required correction. The calculation of this correction only requires knowledge of basic sample and detector data. The uncertainty of the reported activity can then also be assessed and is influenced by the uncertainty of the efficiency evaluated around its new, corrected value. An appropriate expression for this uncertainty has been derived.

Journal Article↗

PubMed2006

The uncertainties associated with the application of batch technique for distribution coefficients determination--a case study of cesium adsorption on four different bentonites.

The uncertainties associated with the batch method used often as adsorption data source for performance assessments of radioactive waste repositories have been analyzed and evaluated. The adsorption of cesium on four different bentonites (two Na- and two Ca-bentonites) using a radiotracer ((137)Cs) technique has been studied to evaluate experimental uncertainties and compare their effects on calculated distribution coefficients (K(d)s). Three main factors influencing uncertainty of K(d) at given conditions were identified-the radiotracer operation (mainly tracer addition to experimental systems), the phase separations efficiency and the mineralogical heterogeneity of samples. It was found that the determination of quantitative contributions of the last two factors to the uncertainty of K(d) is difficult, depending on input material and conditions. The centrifugation and ultrafiltration method has been tested for removing colloids in sample solutions, but the results obtained were disputable. The mineral heterogeneity (complex mineral composition) effect has been identified mainly in kinetics of cesium adsorption where three different trends were described. This has important influence on the time-scale of the experiment's planning and equilibrium time estimation or identification. It has been concluded that experimental procedure may represent important uncertainty source of calculated K(d). In performance assessment studies, this uncertainty of K(d) given by the appropriate experimental procedure should be taken into account and properly evaluated.

Journal Article↗

PubMed2006

Uncertainty of calculation results in vehicle collision analysis.

In the analysis of road accidents two types of calculation result uncertainty can be distinguished: modelling uncertainty and uncertainty in calculation results [R.M. Brach, M. Brach, Vehicle Accident Analysis & Reconstruction Methods, SAE International Publisher, Warrendale, 2005]. The problem becomes very important first of all when minor modifications of input parameters or application of different models of the phenomenon lead to a fundamentally different answer to the question posed by the court. The aim of the paper was to prove the necessity of including the problem of uncertainty in calculations related to vehicle collision mechanics and to justify the application of different error analysis methods recommendable in vehicle collision reconstruction. The data file from crash test No. 7 [H. Burg, M. Lindenmann, Unfallversuche, Verlag Information Ambs, Kippenheim, 1982] was used, the selection restricted to the range typical of average police records of collision place. Collision speeds were calculated using two methods: reconstruction and simulation. The analysis of uncertainty was carried out. Maximum and mean square uncertainty were calculated by means of total differential of relevant forms. Since the reconstruction resulted in very broad error intervals of uniform distribution, additional calculations were performed by the Monte Carlo method using algorithm described in [W. Wach, J. Unarski, Determination of vehicle velocities and collision location by means of Monte Carlo simulation method, Special Publication Accident Reconstruction SP-1999, SAE Paper No. 2006-01-0907, 2006].

Journal Article↗

PubMed2004

Reducing family members' anxiety and uncertainty in illness around transfer from intensive care: an intervention study.

INTRODUCTION: This intervention study examines anxiety and uncertainty in illness in families transferring from intensive care to a general ward. METHODS: The pre-test, post-test design purposively allocated family members to a control (n = 80) and intervention group (n = 82). The intervention group experienced a structured individualised transfer method whereas the control group received existing ad hoc transfer methods. Families were surveyed before and after transfer. RESULTS: Families' uncertainty was significantly related to their state anxiety (P < 0.000), the relationship to the patient (P = 0.022), and the unexpected nature of patients' admission (P < 0.000). Anxiety increased significantly with reduced social support (P = 0.002). Following transfer, anxiety reduced significantly for both groups whereas uncertainty reduced significantly for the intervention group (P = 0.03). CONCLUSION: Families at the time of transfer experience uncertainty and anxiety, which are significantly related in this study. The intervention significantly reduced uncertainty scores. When the family member was a parent, when admissions were unexpected, and those with fewer social supports represent potential 'at risk' groups whose adaptation to transfer may limit their coping ability. The structured individualised method of transfer is recommended with further research of ICU families to further examine the dimension of uncertainty and how it affects patient outcomes.

Adolescent↗

PubMed2001

Experimental studies of uncertainties associated with chromatographic techniques.

The paper describes experiments for the evaluation of uncertainties associated with a number of chromatographic parameters. Studies of the analysis of vitamins by HPLC illustrate the estimation of the uncertainties associated with experimental "input" parameters such as the detector wavelength, column temperature and mobile phase flow-rate. Experimental design techniques, which allow the efficient study a number of parameters simultaneously, are described. Multiple linear regression was used to fit response surfaces to the data. The resulting equations were used in the estimation of the uncertainties. Three approaches to uncertainty calculation were compared--Kragten's spreadsheet, symmetric spreadsheet and algebraic differentiation. In cases where non-linearity in the model was significant, agreement between the uncertainty estimates was poor as the spreadsheet approaches do not include second-order uncertainty terms.

Artifacts↗

PubMed2000

The influence on partial order ranking from input parameter uncertainty. Definition of a robustness parameter.

The method of partial order ranking has been used within the environmental area for a variety of purposes as an attractive way of handling complex information. However, the environmental data are often associated with a significant degree of uncertainty. In this investigation the general nature of the influence from data uncertainty on the partial order ranking is analyzed. A Monte Carlo type analysis is performed in which a series of randomly formed data are used to test the influence of data uncertainty. The partial order ranking is interpreted, where the results are transferred to a one-dimensional ranking scale taking into account that not all elements are ranked with the same certainty. A simple general robustness parameter (E) in form of the expected number of comparisons for each ranking element is defined and correlated to the uncertainty analysis results. A simple equation relates E to the number of elements and the number of parameters, respectively. The magnitude of the ranking uncertainty is shown to increase rapidly when the E value decreases below 4-5 comparisons per element. When the E value exceeds 5 the ranking uncertainty becomes nearly constant and independent on the actual E value.

Environmental Monitoring↗

PubMed2001

Considering uncertainty in comparing the burden of illness due to foodborne microbial pathogens.

The uncertainty attendant to burden-of-illness estimates should be taken into account in comparing the public health impact of different foodborne pathogens. In this paper, decision analysis concepts are applied to the comparisons of pathogen-specific burden-of-illness estimates. In situations wherein the magnitude of uncertainty varies, the rank order of pathogen-specific burden-of-illness estimates is sensitive to the decisional criteria applied. To illustrate the magnitude of attendant uncertainty in pathogen-specific foodborne-illness estimates, probabilistic risk assessment methods are used to characterize the uncertainty regarding the burden of illness due to Escherichia coli O157:H7. The magnitude of uncertainty about the burden of food-related illness due to E. coli O157:H7 is substantial, ranging from less than 50,000 to more than 120,000 cases/year. This example underscores the importance of considering the uncertainty attendant to burden-of-illness estimates in comparing the public health impacts of different pathogens. Although some would argue that the expected value of the number of illnesses provides the "best estimate" for decision-making, this merely reflects a decision-making rule of convention and not a scientific truism.

Decision Trees↗

PubMedDate not supplied

Radionuclide transport simulation and uncertainty analyses with the saturated-zone site-scale model at Yucca Mountain, Nevada.

Evaluation of radionuclide transport in the saturated zone (SZ) to the accessible environment is an important component of performance assessment for the proposed radioactive waste repository at Yucca Mountain. Simulations of radionuclide migration in the SZ have been performed using the calibrated three-dimensional (3-D) SZ site-scale flow and transport model. An innovative particle-tracking method was used to simulate transport that includes the processes of advection, dispersion, matrix diffusion, and sorption. The uncertainties in groundwater flow and radionuclide transport were quantitatively evaluated to develop uncertainty distributions for key model parameters, and multiple realizations of the SZ system were simulated using the SZ site-scale model. The results of multiple realizations of radionuclide transport indicate significant aggregate uncertainty in transport times through the SZ. The simulated radionuclide mass breakthrough curves in the SZ have been coupled with other components of the repository system in Total System Performance Assessment (TSPA) analyses and constitute the means by which uncertainty in the SZ is incorporated into regulatory analyses. Regression analysis has been used to determine the sensitivity of radionuclide transport simulation results to the uncertainty of individual model input parameters. Results of the sensitivity analysis indicate that median radionuclide transport times were dominantly controlled by uncertainty in the specific discharge in the SZ, with sorption and retardation in the alluvium playing important roles for some radionuclides.

Forecasting↗

PubMed2000

From "reducing" to "coping with" uncertainty: reconceptualizing the central challenge in breast self-exams.

An ideology of uncertainty reduction pervades scholarly and popular discourse on breast self-exams (BSE). Women are encouraged to understand BSE as an activity that reduces uncertainty about their health. Moreover, uncertainties about the procedure itself are conceived as barriers to BSE. In turn, reducing these uncertainties is seen as the key to promoting BSE. We argue that the ideology of uncertainty reduction is both descriptively and prescriptively inadequate and potentially a threat to women's health. We further contend the ideology should be replaced by a framework that illuminates processes of coping with uncertainty. Several major characteristics of such a framework, as well as implications for medical practice, are discussed and illustrated within the context of BSE.

Adaptation, Psychological↗

PubMed1999

The tabletting machine as an analytical instrument: consequences of uncertainties in punch force and punch separation data on some parameters describing the course of the tabletting process.

The influence of the uncertainties involved in the measurement of punch forces and punch separation in an eccentric tableting machine on the validity of the analytical results was evaluated using six direct compression excipients. The analytical parameters considered were the maximum upper punch pressure, the minimum punch separation, the maximum relative density, the contact time, the area quotient according to Emschermann and Müller, the Weibull and Heckel parameters, as well as the total, expansion and apparent net work. The measuring uncertainties were divided into between-run deviations (BD) and within-run deviations (WD), which are constant and variable, respectively, during a tableting event. Both types of uncertainties were expressed as simple error limits. The effects of the measuring BD's were calculated by adding them to the force and displacement data and then computing the analytical parameters in the conventional way. The estimation of the effects of the measuring WD's needs special methods for each parameter. Their validation showed that they were in most cases able to include the true effects of some exemplary selected errors but tend to overestimate them. From the sum of the confidence interval (CI) of a mean parameter value from repeated tableting experiments, the confidence interval with respect to curve fitting, the BD and the WD of the analytical results, the total deviation (TD) of the results was obtained, which provides a worst case measure of the uncertainties. The TD makes a differentiation between materials with similar tableting behaviour impossible in many cases, thus providing too low a selectivity. The best case uncertainties account for the difference in the response of the data to be compared to the measuring errors. The uncertainty decreases considerably under best case conditions. However, the best case intervals predicted from the worst case limits are not generally valid. Thus, besides the TD, only the CI's remain for the assessment of the analytical results. However, in the presence of systematic errors the statistical analysis cannot assure the correctness of the conclusions drawn with the degree of certainty supposed, even if the systematic measuring errors are the same for the data to be compared.

Chemistry, Pharmaceutical↗

PubMed2003

Predicting events of varying probability: uncertainty investigated by fMRI.

Many everyday life predictions rely on the experience and memory of event frequencies, i.e., natural samplings. We used functional magnetic resonance imaging (fMRI) to investigate the neural substrates of prediction under varying uncertainty based on a natural sampling approach. The study focused particularly on a comparison with other types of externally attributed uncertainty, such as guessing, and on the frontomedian cortex, which is known to be engaged in many types of decisions under uncertainty. On the basis of preceding stimulus cues, participants predicted events that occurred with probabilities ranging from p = 0.6 to p = 1.0. In contrast to certain predictions in a control task, predictions under uncertainty elicited activations within a posterior frontomedian area (mesial BA 8) and within a set of subcortical areas which are known to subserve dopaminergic modulations. The parametric analysis revealed that activation within the mesial BA 8 significantly increased with increasing uncertainty. A comparison with other types of uncertainty indicates that frontomedian correlates of frequency-based prediction appear to be comparable with those induced in long-term stimulus-response adaptation processes such as hypothesis testing, in contrast to those engaged in short-term error processing such as guessing.

Adult↗