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PubMed2005

Uncertainty and precaution in European environmental risk assessment of chemicals.

It is recognised that there is a need for a proper treatment and transparency of uncertainty in risk assessment and management, especially in view of the upcoming proposed new chemical policy REACH, which delegates the responsibility for conducting risk assessments to industry. The current EU risk assessment for new and existing substances is largely deterministic and prudential measures are implicitly embedded in calculation schemes and rules. In this paper, a more probabilistic approach to risk assessment is advocated. The advantage is twofold: 1) inherent variability and other uncertainty pertaining to exposure and effects are transparently taken into account, while at the same time 2) issues of caution are explicitly transferred to the risk management phase. The result of a probabilistic risk assessment as suggested is improved transparency with quantitative and qualitative uncertainty estimates. Such uncertainty information can be used to discuss precautionary measures in the context of risk management.

Decision Making↗
PubMed2006

[Comparison of three approaches for uncertainty estimation].

Three different approaches for the estimation of uncertainty measurements using the same analytical method were compared, namely validation, robustness and inter-laboratory studies. The uncertainty obtained with the robustness study! predicted well the uncertainty of the inter-laboratory study. On the other hand, the uncertainty estimation obtained with the validation study is lower than those obtained with the two other approaches but is still acceptable as long as the analytical method will be used in a single laboratory.

Chromatography, Liquid↗
PubMed1989

Telling the truth in the face of medical uncertainty and disagreement.

The pediatric oncologist often must face medical uncertainty and differing opinions among consultants. This raises a dilemma about telling the truth: Does the ethical requirement for telling the truth include informing parents about uncertainties and disagreements, or does the obligation to protect from emotional burden justify withholding information? Answering this question requires an analysis of the nature of medical disagreements. It is argued that disagreements that arise because of medical uncertainties are not disagreements about facts, but disagreements in attitude, where appeal to expertise is not possible. Thus, treatment recommendations must be offered carefully, in order to avoid imposing values on patients. Physicians should make clear the reasoning behind their recommendations, as well as areas of uncertainty. This approach offers the only possibility for parents to give informed consent and to participate in responsible decision making for their child that is consistent with their own values.

Child↗
PubMed1998

Assessing uncertainty in microsimulation modelling with application to cancer screening interventions.

Microsimulation is fast becoming the approach of choice for modelling and analysing complex processes in the absence of mathematical tractability. While this approach has been developed and promoted in engineering contexts for some time, it has more recently found a place in the mainstream of the study of chronic disease interventions such as cancer screening. The construction of a simulation model requires the specification of a model structure and sets of parameter values, both of which may have a considerable amount of uncertainty associated with them. This uncertainty is rarely quantified when reporting micro-simulation results. We suggest a Bayesian approach and assume a parametric probability distribution to mathematically express the uncertainty related to model parameters. First, we design a simulation experiment to achieve good coverage of the parameter space. Second, we model a response surface for the outcome of interest as a function of the model parameters using the simulation results. Third, we summarize the variability in the outcome of interest, including variation due to parameter uncertainty, using the response surface in combination with parameter probability distributions. We illustrate the proposed method with an application of a microsimulator designed to investigate the effect of prostate specific antigen (PSA) screening on prostate cancer mortality rates.

Adult↗
PubMed1993

Predictors of psychosocial adjustment in systemic sclerosis. The influence of formal education level, functional ability, hardiness, uncertainty, and social support.

OBJECTIVE: To determine predictors of psychosocial adjustment in patients with systemic sclerosis (SSc). METHODS: We surveyed 94 patients with SSc. Age, sex, education level, marital status, work status, income, support group attendance, length of time since diagnosis, functional status, social support, illness-related uncertainty, and hardiness were examined as potential predictors of psychosocial adjustment. The reliability and validity of the instruments used to measure these variables have been established. RESULTS: Only education level, functional ability, illness-related uncertainty, hardiness, and social support were predictive of psychosocial adjustment. Education level and functional ability explained 14% of the variance in psychosocial adjustment, while illness-related uncertainty, hardiness, and social support increased the explained variance to 38%. CONCLUSION: Although patients with relatively poorer psychosocial adjustment to illness have lower formal education levels and more functional disability, the majority of the explained variance in psychosocial adjustment is ascribable to illness-related uncertainty, low level of hardiness, and less satisfaction with social support.

Adaptation, Psychological↗
PubMed2002

Helping patients with localized prostate carcinoma manage uncertainty and treatment side effects: nurse-delivered psychoeducational intervention over the telephone.

BACKGROUND: The objective of this study was to test the efficacy of an individualized uncertainty management intervention delivered by telephone to Caucasian and African-American men with localized prostate carcinoma and directed at managing the uncertainties of their disease and treatment. METHODS: The authors delivered a psychoeducational intervention by phone to men with prostate carcinoma, with or without supplemented delivery to a close family member, that was directed at managing uncertainty and improving symptom control. One hundred thirty-four Caucasian men and 105 African-American men were assigned randomly to one of two approaches to delivering the intervention or to the control condition. Men entered the study immediately after surgical treatment or in the first 3 weeks of radiation therapy. Trained nurses delivered the intervention through weekly phone calls for 8 weeks. RESULTS: The authors found that the majority of intervention effects were from baseline to 4 months postbaseline, when treatment side effects are most intense. Both Caucasian men and African-American men who received either one of the two approaches for delivering the intervention improved in the two uncertainty management methods of cognitive reframing and problem solving. Similarly, when the intervention groups were combined, men who received the intervention also improved significantly in control of incontinence by 4 months postbaseline. Decreases in the number of treatment side effects differed by time and treatment/ ethnic group interactions as did satisfaction with sexual functioning. CONCLUSIONS: This is one of the first tests of a psychoeducational intervention among men with prostate carcinoma and was the first test that included a sufficient number of African-American men to test by ethnic group. Therefore, replication of these findings is advised.

Black or African American↗
PubMed2005

Quantitative magnetic resonance spectroscopy: semi-parametric modeling and determination of uncertainties.

A semi-parametric approach for the quantitative analysis of magnetic resonance (MR) spectra is proposed and an uncertainty analysis is given. Single resonances are described by parametric models or by parametrized in vitro spectra and the baseline is determined nonparametrically by regularization. By viewing baseline estimation in a reproducing kernel Hilbert space, an explicit parametric solution for the baseline is derived. A Bayesian point of view is adopted to derive uncertainties, and the many parameters associated with the baseline solution are treated as nuisance parameters. The derived uncertainties formally reduce to Cramér-Rao lower bounds for the parametric part of the model in the case of a vanishing baseline. The proposed uncertainty calculation was applied to simulated and measured MR spectra and the results were compared to Cramér-Rao lower bounds derived after the nonparametrically estimated baselines were subtracted from the spectra. In particular, for high SNR and strong baseline contributions the proposed procedure yields a more appropriate characterization of the accuracy of parameter estimates than Crémer-Rao lower bounds, which tend to overestimate accuracy.

Bayes Theorem↗
PubMed1988

Uncertainty, coping, and distress following myocardial infarction: transition from hospital to home.

The purpose of this study was to examine the influence of uncertainty in illness and use of coping methods on emotional distress and recovery following myocardial infarction. A longitudinal exploratory design with measures obtained at three times was used; multiple regression was used to analyze the data. Uncertainty explained a significant amount of the variance in emotional distress prior to hospital discharge (21%), and 1 (16%) and 4 (26%) weeks after discharge. Patients reporting greater uncertainty also reported more emotional distress. One week after discharge, coping behaviors significantly added to the variance explained in distress (27%). Greater use of emotive coping behaviors was associated with higher levels of emotional distress and accounted for the majority of the variance explained by coping behaviors (23%). The findings are discussed in terms of the nature of uncertainty in health care and future model development.

Adaptation, Psychological↗
PubMed2004

Uncertainty and the value of diagnostic information, with application to axillary lymph node dissection in breast cancer.

In clinical decision making, it is common to ask whether, and how much, a diagnostic procedure is contributing to subsequent treatment decisions. Statistically, quantification of the value of the information provided by a diagnostic procedure can be carried out using decision trees with multiple decision points, representing both the diagnostic test and the subsequent treatments that may depend on the test's results. This article investigates probabilistic sensitivity analysis approaches for exploring and communicating parameter uncertainty in such decision trees. Complexities arise because uncertainty about a model's inputs determines uncertainty about optimal decisions at all decision nodes of a tree. We present the expected utility solution strategy for multistage decision problems in the presence of uncertainty on input parameters, propose a set of graphical displays and summarization tools for probabilistic sensitivity analysis in multistage decision trees, and provide an application to axillary lymph node dissection in breast cancer.

Axilla↗
PubMed1998

Evaluation of the uncertainty factor for subchronic-to-chronic extrapolation: statistical analysis of toxicity data.

For the extrapolation of a subchronic no-observed-adverse-effect level (NOAEL) to a chronic NOAEL an uncertainty factor of 10 is routinely applied. We evaluated this uncertainty factor by statistically analyzing a database comprising 149 oral NOAEL(subchronic)/NOAEL(chronic) ratios. Since any database forms only a limited sample of all existent chemicals, we believe that estimation errors should be taken into account. Therefore, in addition to the 95th percentile (P95) of the ratio distribution, we calculated the 95% confidence interval (CI) of this percentile. The geometric mean (GM), geometric standard deviation (GSD), P95, and CI were 1.7, 5.6, 29, and 20-46, respectively. These data do not support a lowering of the uncertainty factor as has been suggested by others. Furthermore, we analyzed the LOAEL/NOAEL ratio for subacute, subchronic, and chronic toxicity studies. However, the size of the LOAEL/NOAEL ratio only depends on the spacing between doses of the studies reviewed. Therefore, though the results may be considered supportive for an uncertainty factor of 10, we believe that there is no justification for the use of such a factor. Instead, we recommend the use of dose-response modeling which would make LOAEL-to-NOAEL extrapolation redundant.

Administration, Oral↗
PubMed1999

Addressing human variability in risk assessment--the robustness of the intraspecies uncertainty factor.

Addressing human variability and sensitive subpopulations is one of the challenges of risk assessment and is an important aspect of the Food Quality Protection Act, the law passed in 1996 that regulates food use pesticides in the United States. The intraspecies uncertainty factor is intended to address differences in susceptibility within the human population. This paper examines the history and scientific basis for the intraspecies uncertainty factor. Our best source of knowledge about human variability in the response to chemicals comes from clinical trials of pharmaceuticals. This large body of data allows both qualitative and quantitative characterization of variability in pharmacokinetic and pharmacodynamic parameters in the general population and in subgroups such as children. The preponderance of evidence in the areas of pharmacodynamics and pharmacokinetics supports the routine use of an intraspecies uncertainty factor in the range of 1-10 as being protective of greater than 99% of the human population. The intraspecies uncertainty factor is highly protective of various subpopulations, including infants and children.

Animals↗
PubMedDate not supplied

Estimation of basic uncertainties in clinical analysis.

Clinical analyses have a vital importance in human health. Thus, it is necessary to have reliable analytical information which depends on a good assessment of accuracy and this can be obtained by minimization of uncertainty values. The uncertainty values are complex and arise from different sources such as sample, method, instrumentation and data processing. Some of these components may have been evaluated from the distribution of results of series of measurements and can be characterized by standard deviations. In our laboratory, for example the balance calibration uncertainty for 1 g was found to be 0.00414 g. The uncertainties for the volume of solution contained in a 100 mL volumetric flask and a 0.5 mL glass-pipette were calculated to be 0.0843 mL and 0.0071 mL respectively and etc.

Calibration↗
PubMed2002

Secondary pH standards and their uncertainty in the context of the problem of two pH scales.

Establishing a traceability route with all measurement and uncertainty relationships determined is an important aspect of traceability, and seems to be particularly striking in pH measurement. In this paper the issue of evaluation of secondary pH standards measured with reference to a primary standard in a differential cell with free diffusion type liquid junctions is considered. Relatively high uncertainty, U=0.015, has been assigned to such standards in the recent IUPAC Recommendations on pH (2001), because of a specific residual liquid-junction potential treated statistically as a contribution to the combined uncertainty. Close inspection of the problem leads to the conclusion that a correction for the residual liquid-junction potential should be applied to the measured value of a secondary pH standard. This can be considered as a correction for a known systematic effect on the traceability route. With available experimental data it is demonstrated that such a correction can reasonably be made for well-studied standard buffer systems. In this way the uncertainty associated with secondary pH standards is kept to a low level, and, what is more, the problem of two pH scales, a multi-standard scale and a single-standard scale, gains a proper solution. The need for different treatment of residual liquid-junction potentials at different levels in the measurement hierarchy is noted. Much attention is also given to rational categorization of pH standards in the hierarchy.

Journal Article↗
PubMed2003

Uncertainty evaluation of mass values determined by electronic balances in analytical chemistry: a new method to correct for air buoyancy.

A new method to correct for the largest systematic influence in mass determination-air buoyancy-is outlined. A full description of the most relevant influence parameters is given and the combined measurement uncertainty is evaluated according to the ISO-GUM approach [1]. A new correction method for air buoyancy using an artefact is presented. This method has the advantage that only a mass artefact is used to correct for air buoyancy. The classical approach demands the determination of the air density and therefore suitable equipment to measure at least the air temperature, the air pressure and the relative air humidity within the demanded uncertainties (i.e. three independent measurement tasks have to be performed simultaneously). The calculated uncertainty is lower for the classical method. However a field laboratory may not always be in possession of fully traceable measurement systems for these room climatic parameters.A comparison of three approaches applied to the calculation of the combined uncertainty of mass values is presented. Namely the classical determination of air buoyancy, the artefact method, and the neglecting of this systematic effect as proposed in the new EURACHEM/CITAC guide [2]. The artefact method is suitable for high-precision measurement in analytical chemistry and especially for the production of certified reference materials, reference values and analytical chemical reference materials. The method could also be used either for volume determination of solids or for air density measurement by an independent method.

Journal Article↗
PubMed2003

An uncertainty budget for trace analysis by isotope-dilution ICP-MS with proper consideration of correlation.

Isotope-dilution mass spectrometry (IDMS) is considered to be a method without significant correction factors. It is also believed that this method is well understood. But unfortunately a large number of different uncertainty budgets have been published that consider different correction factors. These differences lead to conflicting combined uncertainties especially in trace analysis. It is described how the known correction factors must be considered in the uncertainty budget of values determined by IDMS combined with ICP-MS (ICP-IDMS). The corrections applied are dead time, background, interference, mass discrimination, blank correction and air buoyancy.IDMS measurements consist always of a series of isotope abundance ratio measurements and can be done according to different measurement protocols. Because the measurement protocols of IDMS are often rather sophisticated, correlations of influence quantities are difficult to identify. Therefore the measurement protocol has to be carefully considered in the specification of the measurand and a strategy is presented to properly account for these correlations. This will be exemplified for the estimation of mass fractions of platinum group elements (PGEs) and Re in the geological reference material UB-N (from CRPG-CNRS, Nancy in France) with ICP-IDMS. The PGEs with more than one isotope and the element Re are measured with on-line cation-exchange chromatography coupled to a quadrupole ICP-MS. All contents are below 10 microg kg(-1). Only osmium is separated from the matrix by direct sparging of OsO(4) into the plasma. This leads to transient signals for all PGEs and Re. It is possible to estimate the combined uncertainties and keep them favourably small despite the low contents, the transient signals and the sophisticated correction model.

Journal Article↗
PubMed2006

Comparison of three strategies to evaluate uncertainty from in-house validation data. A case study: mercury determination in sediments.

In the present paper, three approaches are compared for the evaluation of the combined uncertainty in the determination of mercury in aquatic sediments by an aqua regia extraction procedure. For this, the data obtained in validation studies from five certified reference materials (CRMs), covering a range of concentrations from 0.8 to 130 mg kg(-1) of mercury and analysed by three atomic spectroscopic techniques (cold vapour generation atomic fluorescence spectrometry, CV-AFS, cold vapour generation atomic absorption spectroscopy, and inductively coupled plasma mass spectroscopy), were considered. The combined uncertainty was firstly assessed by considering separately the data obtained for each CRM analysed (approach A). Moreover, this assessment was also performed with two other calculation approaches (B and C) based on the pooled data obtained from the validation step. The comparison of the results obtained for the different techniques showed a clear bias effect when using CV-AFS with nitric acid as a diluent. In relation to the strategies tested for the combined uncertainty assessment, approach C proved to be the easiest and friendliest method for uncertainty assessment.

Journal Article↗
PubMed1985

The analysis of ligand-binding data with experimental uncertainties in the independent variables.

The method of experimental data analysis known as least-squares requires several inherent assumptions to be met in order for the analysis to be statistically correct. In particular, it must be assumed that the experimental uncertainties exist only on the dependent variables. Least-squares is often used for applications where this assumption is not satisfied. An alternative method of data analysis circumvents the assumption that no experimental uncertainty exists in the independent variables. This method, known as maximum likelihood, will produce statistically correct results in cases where experimental uncertainty exists on both the dependent and independent variables. The method can easily be generalized to include cases where the dependent and independent variables are cross-correlated. The method can also be generalized to include non-Gaussian distributions of experimental uncertainties. The examples presented are simulated applications to ligand-binding problems. The general method is, however, applicable to a wide range of problems in biochemistry.

Binding Sites↗
PubMed1989

The propagation of uncertainty in human mortality processes operating in stochastic environments.

This paper presents a model describing how the uncertainty due to influential exogenous processes combines with stochasticity intrinsic to physiological aging processes and propagates through time to generate uncertainty about the future physiological state of the population. Variance expressions are derived for (a) the future values of the physiological variables under the assumption that external factors evolve under a linear stochastic diffusion process, and (b) the cohort survival functions and cohort life expectancies which reflect the uncertainty in the future values of the physiological variables. The model implies that a major component of uncertainty in forecasts of the physiological characteristics of a closed cohort is due to differential rates of survival associated with different realizations of the external process. This suggests that the limits to forecasting may be different in physiological systems subject to systematic mortality than in physical systems such as weather where the concepts of closed cohorts and of mortality selection have no simple analog.

Aging↗