SEARCH · PubMed Health

Results for “Uncertainty”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 343 records · Page 19Linked to original sources

PubMed2005

Effect of uncertainty about population parameters on pharmacodynamics-based prediction of clinical trial power.

Clinical trial simulation (CTS) may be applied to predict power of intended drug trials on the basis of pharmacokinetic/pharmacodynamic (PKPD) drug models. The validity of such predictions will, among other factors, depend on the degree of uncertainty about population parameters entering the simulation. In the current article, we illustrate how population parameter uncertainty may be incorporated in the overall simulation model, using a worked example to demonstrate our approach. Moreover, we suggest an ANOVA-based method for sensitivity analysis, aimed at distinguishing important population parameters, required to be input in the model with a low degree of uncertainty for precise power predictions, from unimportant parameters, which may be entered with a high degree of uncertainty without affecting the reliability of predictions. Our results from simulations with different settings of hyperparameters and doses suggest that indices derived from this type of sensitivity analysis may be used for grading the influence on prediction quality of uncertainty about different population parameters and, thus, facilitate the allocation of resources expended for the preparation of a successful CTS project.

Computer Simulation↗

PubMed2006

A critical review of measurement uncertainty in the enumeration of food micro-organisms.

Derivation of uncertainty provides a way to standardize the expression of variability associated with any analytical procedure. The published information on uncertainty associated with data obtained using microbiological procedures is reviewed to highlight the causes and magnitude of such variability in food microbiology. We also suggest statistical procedures that can be used to assess variability (and hence, uncertainty), within and between laboratories, including procedures that can be used routinely by microbiologists examining foods, and the use of 'robust' methods which allow the retention of 'outlying' data. Although concerned primarily with variability associated with colony count procedures, we discuss also the causes of variability in presence/absence and indirect methods, such as limiting dilution, most probable number and modern instrumental methods of microbiological examination. Recommendations are also made concerning the most important precautions to be taken in order to minimize uncertainty in microbiology. These include strict internal controls at all stages of microbiological testing, as well as validation of methods, trend analysis, use of reference materials and participation in proficiency testing schemes. It is emphasized that the distribution of microbes in foods is inherently heterogeneous, and that this review only addresses uncertainty of measurement with respect to the sample taken, not the lot or consignment of food from which the sample was taken.

Analysis of Variance↗

PubMedDate not supplied

Long-term quality of life and uncertainty in patients living with an implantable cardioverter defibrillator.

PURPOSE: This study describes the quality of life (QOL) and uncertainty in patients who have an implantable cardioverter defibrillator (ICD) and predicts QOL at long-term follow-up. METHODS: Long-term follow-up was defined as 6.9 years +/- 1 year (range 4.11-8.7 years). QOL was measured with the Quality of Life Index, and uncertainty was measured with the Mishel Uncertainty in Illness Scale. RESULTS: The overall QOL and health/functioning were unchanged over time. QOL in the socioeconomic (P = .002) and psychologic/spiritual domains (P = .012) decreased in the first year. From baseline to long-term follow-up, the QOL in the family domain (P = .011) and uncertainty (P = .002) decreased. Uncertainty was a predictor of low QOL. CONCLUSION: QOL was reasonably good 6.9 years post-ICD implantation. Patients felt less uncertain once they had passed the first year of their illness.

Arrhythmias, Cardiac↗

PubMed2006

Quantitative estimation of uncertainty in human risk analysis.

This paper is aimed to candidate the use of an ISO standard procedure (Guide to the Expression of Uncertainty in Measurement, GUM) for quantitative evaluation of uncertainty in Human Risk estimation under chronic exposure to a hazardous chemical compound. Risk was evaluated by using the usual methodologies: the deterministic reasonable maximum exposure (RME) and the statistical Monte Carlo method; in both cases the procedures to evaluate the uncertainty on risk values are detailed. The paper put in evidence that the procedure is able to single out the variables that contribute mostly to the uncertainty. The obtained results show that the application of GUM procedure is easy and straightforward to estimate the uncertainty value on the results of risk estimation. The procedure is applied to a real case concerning the ingestion of milk contaminated by dioxins in a northern part of Italy; the risk value resulted to be over the minimal threshold of 10(-6) with 20-80% confidence.

Animals↗

PubMed2006

Living without labels: the interactional management of diagnostic uncertainty in the genetic counselling clinic.

In the genetic counselling setting it is not uncommon for a client and genetic counsellor to be faced with uncertainty surrounding the exact diagnostic label to be assigned to the client's symptoms. The huge range of possible conditions/syndromes and the lack of definitive evidence available often combine to create diagnostic uncertainty or non-diagnosis (the assessment given where a genetic diagnosis of the client's symptoms cannot be confirmed at that point). This paper aims to explore the interactional management and negotiation of diagnostic uncertainty in the genetic counselling clinic in the UK. Through the application of discourse analytic tools (including reported speech, contrast and hedging) to transcripts of actual clinical interactions, the participants' use of evidence, and professional and client expertise, are examined and found to be key in the negotiation of diagnostic uncertainty. The complete data set for this research consists of transcripts of 18 clinical encounters between genetic counsellor and client. Two client cases are identified and analysed in detail in order to follow the pattern of interactional management of diagnostic uncertainty throughout the whole interaction. The findings suggest that, unlike other medical settings, clients within genetic counselling are able to actively participate in talk about diagnosis allowing, for the extent of non-diagnosis to be negotiated. This is particularly so during two moments in the interaction: the beginning of the clinic where the agenda is set, and towards the end of the clinic when a form of diagnostic assessment must be made. By providing an insight into the problematic interactional activity of giving a non-diagnosis this paper can contribute to discussions on genetic counselling practice. The analysis in this paper demonstrates how a genetic counsellor can manage the balance between accurate information-giving and empathy towards individual client needs for a diagnosis.

Communication↗

PubMed2004

"Pop-out" of targets modulated in luminance or colour: the effect of intrinsic and extrinsic uncertainty.

Targets defined by attributes such as colour or brightness are said to "pop-out" from a cluttered scene, with little or no dependency on the size of the set to be searched, while search for other attributes can depend strongly on set-size. We measured contrast thresholds for increments and decrements in luminance or colour and show that they increase strongly with set-size (as previously observed for orientation). However, in some conditions, where the potential distractors were not salient visual targets, there was no dependency of set-size at all ("pop-out"). All the data can be modelled by assuming two main sources of uncertainty: the intrinsic uncertainty due to the number of detectors monitored during a specific task and the extrinsic uncertainty introduced by increasing the number of items displayed. The strength of the effect is well explained by a simple signal detection theory "signed-max" model suited for two-tailed tasks [Journal of Vision 2 (8), 559]. The results suggest that "pop-out" is not peculiar to luminance or colour, but may occur in conditions when the intrinsic uncertainty is so high as to saturate the effects of further uncertainty sources.

Attention↗

PubMed2004

Sensory uncertainty governs the extent of audio-visual interaction.

Auditory signals have been shown to exert a marked influence on visual perception in a wide range of tasks. However, the mechanisms of these interactions are, at present, poorly understood. Here we present a series of experiments where a temporal cue within the auditory domain can significantly affect the localisation of a moving visual target. To investigate the mechanism of this interaction, we first modulated the spatial positional uncertainty of the visual target by varying its size. When visual positional uncertainty was low (small target size), auditory signals had little or no influence on perceived visual location. However, with increasing visual uncertainty (larger target sizes), auditory signals exerted a significantly greater influence on perceived visual location. We then altered the temporal profile of the auditory signal by modulating the spread of its Gaussian temporal envelope. Introducing this temporal uncertainty to the auditory signal greatly reduced its effect on visual localisation judgements. These findings support the view that the relative uncertainty in individual sensory domains governs the perceptual outcome of multisensory integration.

Acoustic Stimulation↗

PubMed2004

The importance of accounting for the uncertainty of published prognostic model estimates.

OBJECTIVES: Reported is the importance of properly reflecting uncertainty associated with prognostic model estimates when calculating the survival benefit of a treatment or technology, using liver transplantation as an example. METHODS: Monte Carlo simulation techniques were used to account for the uncertainty of prognostic model estimates using the standard errors of the regression coefficients and their correlations. These methods were applied to patients with primary biliary cirrhosis undergoing liver transplantation using a prognostic model from a historic cohort who did not undergo transplantation. The survival gain over 4 years from transplantation was estimated. RESULTS: Ignoring the uncertainty in the prognostic model, the estimated survival benefit of liver transplantation was 16.7 months (95 percent confidence interval [CI], 13.5 to 20.1), and was statistically significant (p < .001). After adjusting for model uncertainty using the standard errors of the regression coefficients, the estimated survival benefit was 17.5 months (95 percent CI, -3.9 to 38.5) and was no longer statistically significant. An additional adjustment for the correlation between regression coefficients widened the 95 percent confidence interval slightly: the estimated survival benefit was 17.0 months (95 percent CI: -4.6 to 38.6). CONCLUSIONS: It is important that the precision of regression coefficients is available for users of published prognostic models. Ignoring this additional information substantially underestimates uncertainty, which can then impact misleadingly on policy decisions.

Cohort Studies↗

PubMed2005

Treatment of bias in estimating measurement uncertainty.

Bias in an analytical measurement should be estimated and corrected for, but this is not always done. As an alternative to correction, there are a number of methods that increase the expanded uncertainty to take account of bias. All sensible combinations of correcting or enlarging uncertainty for bias, whether considered significant or not, were modeled by a Latin hypercube simulation of 125,000 iterations for a range of bias values. The fraction of results for which the result and its expanded uncertainty contained the true value of a simulated test measure and was used to assess the different methods. The strategy of estimating the bias and always correcting is consistently the best throughout the range of biases. For expansion of the uncertainty when the bias is considered significant is best done by SUMU(Max):U(C(test result))=ku(c)(C(test result))+ |delta(run)|, where k is the coverage factor (= 2 for 95% confidence interval), u(c) is the combined standard uncertainty of the measurement and delta(run) is the run bias.

Bias↗

PubMed2006

Assessment of uncertainty in a probabilistic model of consumer exposure to pesticide residues in food.

The assessment of consumer exposure to pesticides is an important part of pesticide regulation. Probabilistic modelling allows analysis of uncertainty and variability in risk assessments. The output of any assessment will be influenced by the characteristics and uncertainty of the inputs, model structure and assumptions. While the use of probabilistic models is well established in the United States, in Europe problems of low acceptance, sparse data and lack of guidelines are slowing the development. The analyses in the current paper focused on the dietary pathway and the exposure of UK toddlers. Three single food, single pesticide case studies were used to parameterize a simple probabilistic model built in Crystal Ball. Data on dietary consumption patterns were extracted from National Diet and Nutrition Surveys, and levels of pesticide active ingredients in foods were collected from Pesticide Residues Committee monitoring. The effect of uncertainty on the exposure estimate was analysed using scenarios, reflecting different assumptions related to sources of uncertainty. The most influential uncertainty issue was the distribution type used to represent input variables. Other sources that most affected model output were non-detects, unit-to-unit variability and processing. Specifying correlation between variables was found to have little effect on exposure estimates. The findings have important implications for how probabilistic modelling should be conducted, communicated and used by policy and decision makers as part of consumer risk assessment of pesticides.

Body Weight↗

PubMed2006

Uncertainty analysis of integrated gasification combined cycle systems based on Frame 7H versus 7F gas turbines.

Integrated gasification combined cycle (IGCC) technology is a promising alternative for clean generation of power and coproduction of chemicals from coal and other feedstocks. Advanced concepts for IGCC systems that incorporate state-of-the-art gas turbine systems, however, are not commercially demonstrated. Therefore, there is uncertainty regarding the future commercial-scale performance, emissions, and cost of such technologies. The Frame 7F gas turbine represents current state-of-practice, whereas the Frame 7H is the most recently introduced advanced commercial gas turbine. The objective of this study was to evaluate the risks and potential payoffs of IGCC technology based on different gas turbine combined cycle designs. Models of entrained-flow gasifier-based IGCC systems with Frame 7F (IGCC-7F) and 7H gas turbine combined cycles (IGCC-7H) were developed in ASPEN Plus. An uncertainty analysis was conducted. Gasifier carbon conversion and project cost uncertainty are identified as the most important uncertain inputs with respect to system performance and cost. The uncertainties in the difference of the efficiencies and costs for the two systems are characterized. Despite uncertainty, the IGCC-7H system is robustly preferred to the IGCC-7F system. Advances in gas turbine design will improve the performance, emissions, and cost of IGCC systems. The implications of this study for decision-making regarding technology selection, research planning, and plant operation are discussed.

Coal↗

PubMed2004

Intra-assay total uncertainty of results in immunoassay techniques.

Uncertainty is a parameter associated with the result of a measurement; this parameter characterizes the dispersion of the values that could reasonably be attributed to the sample. Data processing methods do not take into account the influence of the imprecision and deviation of the experimental points of the calibration system and their impact on the final result of a sample analysis. The aim of this work is: (a) to propose, for each run, a simple method to calculate the uncertainty due to the calibration system (Uc); and (b) to present a method to determine the "intra-assay total uncertainty" (Ut) and evaluate its impact on the final result for an analyte. Ten replicates of standards, controls, and two serum-male and female samples were measured in the same run with a manual kit for determination of testosterone. To calculate Ut, random duplicate responses were selected. For controls and samples, Ut was affected by Uc (2.91% to 6.59%) and by the uncertainty of the measurement of the sample (Us) (1.01 to 8.73%); this allowed us to determine that Ut had values from 3.73% to 9.87%. While Us affects the result of a given sample, Uc affects the result of all the samples with a similar response (cpm). In the method proposed, Ut involves Us and Uc, both factors that introduce variations into the result of a sample by random causes. Intraassay total uncertainty includes the most probable result for the analytical methodology selected.

Bias↗

PubMedDate not supplied

Uncertainty appraisal coping and quality of life in breast cancer survivors.

Breast cancer survivors increasingly experience long-term side effects that influence their quality of life. They also experience uncertainty of their future due to recurrence of disease. Descriptive design was conducted. Using convenience sampling, 150 breast cancer survivors of more than 3 years from time of diagnosis were recruited from Maharaj Nakorn Chiang Mai Hospital, Chiang Mai, Thailand. Research instruments included Mishel Uncertainty in Illness Scale, Stress Appraisal Index, Ways of Coping Questionnaire, and Quality of Life: Breast Cancer Version Questionnaire and Demographic Data Questionnaire. Results revealed that breast cancer survivors had moderate levels of uncertainty in their illness. Survivors appraised their illness and found high level of challenges, moderate level of threat, and low level of harm. Overall quality of life was found to be moderate. Among Ways of Coping strategies, seeking social support was used the most and confrontive coping was used the least. Using hierarchical multiple regression, variables influencing quality of life were year of survival, uncertainty in illness, and harm appraisal. All 3 variables explained 21.8% variance of quality of life. Uncertainty and harm appraisal influence quality of life in breast cancer survivors. Suggestions and further implications were included.

Adaptation, Psychological↗

PubMedDate not supplied

Uncertainty, posttraumatic stress, and health behavior in young adult childhood cancer survivors.

BACKGROUND: Young adult survivors of childhood cancer are at risk for medical late effects, some of which can be managed through health promotion behaviors. However, chronic uncertainty about the future can lead to the development of posttraumatic stress symptoms (PTSS) that can interfere with health promotion behaviors. OBJECTIVES: To test a mediating model for the relationships among uncertainty, PTSS, and health promotion behaviors in young adult survivors of childhood cancer. METHODS: The design was cross-sectional correlational. A convenience sample was used, and the data were collected using a mailed survey. Study measures included the Mishel Uncertainty in Illness Scale-Community Form, the Posttraumatic Stress Disorder Index, and the Health Promoting Lifestyle Profile II. RESULTS: Forty-six (51.1%) of the eligible survivors responded to the invitation to participate in the study. The analysis was based on data from 45 survivors. The results show that the relationship between PTSS and health promotion behaviors was mediated by uncertainty. DISCUSSION: Uncertainty is a suitable target for theory-based nursing interventions used to boost health promotion behaviors in young adult survivors of childhood cancer.

Adult↗

PubMed2005

Relocation into a new building and its effect on uncertainty and anxiety among psychiatric patients.

The study was designed to investigate the relationship between uncertainty and state anxiety among psychiatric patients before the closed wards of a psychiatric hospital were relocated to new premises. Patients from four psychiatric departments completed a structured questionnaire a week before, and six weeks after, relocation. Inter-variable relationships were assessed by Pearson correlation coefficients. The participants demonstrated moderate levels of pre-relocation uncertainty and anxiety. A significant correlation was found between anxiety and uncertainty both before and after the relocation. Anxiety after the relocation was significantly lower. There was statistical association between uncertainty and state anxiety. This study highlights the need to prepare patients and provide interventions relieving anxiety and lowering uncertainty before environmentally stressful events, such as relocation to a new building.

Adult↗

PubMed2006

Uncertain numbers and uncertainty in the selection of input distributions--consequences for a probabilistic risk assessment of contaminated land.

Risks from exposure to contaminated land are often assessed with the aid of mathematical models. The current probabilistic approach is a considerable improvement on previous deterministic risk assessment practices, in that it attempts to characterize uncertainty and variability. However, some inputs continue to be assigned as precise numbers, while others are characterized as precise probability distributions. Such precision is hard to justify, and we show in this article how rounding errors and distribution assumptions can affect an exposure assessment. The outcome of traditional deterministic point estimates and Monte Carlo simulations were compared to probability bounds analyses. Assigning all scalars as imprecise numbers (intervals prescribed by significant digits) added uncertainty to the deterministic point estimate of about one order of magnitude. Similarly, representing probability distributions as probability boxes added several orders of magnitude to the uncertainty of the probabilistic estimate. This indicates that the size of the uncertainty in such assessments is actually much greater than currently reported. The article suggests that full disclosure of the uncertainty may facilitate decision making in opening up a negotiation window. In the risk analysis process, it is also an ethical obligation to clarify the boundary between the scientific and social domains.

Body Weight↗

PubMed2005

Risk, rationality, and regret: responding to the uncertainty of childhood food anaphylaxis.

Risk and uncertainty are unavoidable in clinical medicine. In the case of childhood food allergy, the dysphoric experience of uncertainty is heightened by the perception of unpredictable danger to young children. Medicine has tended to respond to uncertainty with forms of rational decision making. Rationality cannot, however, resolve uncertainty and provides an insufficient account of risk. This paper compares the medical and parental accounts of two peanut allergic toddlers to highlight the value of emotions in decision making. One emotion in particular, regret, assists in explaining the actions taken to prevent allergic reactions, given the diffuse nature of responsibility for children. In this light, the assumption that doctors make rational judgments while patients have emotion led preferences is a false dichotomy. Reconciling medical and lay accounts requires acknowledgement of the interrelationship between the rational and the emotional, and may lead to more appropriate clinical decision making under conditions of uncertainty.

Anaphylaxis↗

PubMed2003

Doubly distributional population codes: simultaneous representation of uncertainty and multiplicity.

Perceptual inference fundamentally involves uncertainty, arising from noise in sensation and the ill-posed nature of many perceptual problems. Accurate perception requires that this uncertainty be correctly represented, manipulated, and learned about. The choices subjects make in various psychophysical experiments suggest that they do indeed take such uncertainty into account when making perceptual inferences, posing the question as to how uncertainty is represented in the activities of neuronal populations. Most theoretical investigations of population coding have ignored this issue altogether; the few existing proposals that address it do so in such a way that it is fatally conflated with another facet of perceptual problems that also needs correct handling: multiplicity (that is, the simultaneous presence of multiple distinct stimuli). We present and validate a more powerful proposal for the way that population activity may encode uncertainty, both distinctly from and simultaneously with multiplicity.

Action Potentials↗