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PubMed1985

Uncertainty explains many aspects of visual contrast detection and discrimination.

More than 20 years ago, Tanner [Ann. N.Y. Acad. Sci. 89, 752 (1961)] noted that observers asked to detect a signal act as though they are uncertain about the physical characteristics of the signal to be detected. The popular assumptions of probability summation and decision variable, taken together, imply this uncertainty. This paper defines and uncertainty model of visual detection that assumes that the observer is uncertain among many signals and chooses the likeliest. With only four parameters, the uncertainty model explains why d' is approximately a power function of contrast ("nonlinear transduction") and accurately predicts effects of summation, facilitation, noise, subjective criterion, and task for near-threshold contrast. Thus the uncertainty model offers a synthesis of much of our current understanding of visual contrast detection and discrimination.

Attention↗
PubMed1991

Detection uncertainty and the facilitation of chromatic detection by luminance contours.

A suprathreshold luminance flash (1 degree, 200 msec) on a large uniform yellow field facilitates detection of a coincident (1 degree, 200 msec) red or green equiluminant flash and approximately linearizes the psychometric function for detecting the chromatic flash. The facilitation is produced by the suprathreshold contour created by the luminance flash. We tested whether the contour facilitates detection by reducing spatiotemporal uncertainty in detecting the chromatic flash. Uncertainty increase false alarms, and this effect can be factored out by correcting yes-no psychometric functions for guessing. Uncertainty also alters the shape of the receiver operating characteristic. Measurements of yes-no psychometric functions and receiver operating characteristics do not support the uncertainty reduction hypothesis.

Color Perception↗
PubMed2006

Antibiotic timing and diagnostic uncertainty in Medicare patients with pneumonia: is it reasonable to expect all patients to receive antibiotics within 4 hours?

BACKGROUND: Many organizations, including the Centers for Medicare & Medicaid Services, measure the percentage of patients hospitalized with pneumonia who receive antibiotics within 4 h of presentation. Because the diagnosis of pneumonia can be delayed in patients with an atypical presentation, there are concerns that attempts to achieve a performance target of 100% may encourage inappropriate antibiotic usage and the diversion of limited resources from seriously ill patients. This study was performed to determine how frequently Medicare patients with a hospital discharge diagnosis of pneumonia present in a manner that could potentially lead to diagnostic uncertainty and a resulting appropriate delay in antibiotic administration. METHODS: Randomly selected charts of hospitalized Medicare patients who have received diagnoses of pneumonia were reviewed independently by three reviewers to determine whether there was a potential reason for a delay of antibiotic administration other than quality of care. Antibiotic administration timing, patient demographic, and clinical characteristics were also abstracted. RESULTS: Nineteen of 86 patients (22%; 95% confidence interval, 13.7 to 32.2) presented in a manner that had the potential to result in delayed antibiotic treatment due to diagnostic uncertainty. Diagnostic uncertainty was significantly associated with the lack of rales, normal pulse oximetry findings, and lack of an infiltrate seen on the chest radiograph. There was a nonsignificant trend toward a longer time until antibiotic treatment in patients with diagnostic uncertainty. CONCLUSIONS: Many Medicare patients in whom pneumonia has been diagnosed present in an atypical manner. Delivering antibiotic treatment within 4 h for all patients would necessitate the treatment of many patients before a firm diagnosis can be made.

Aged↗
PubMed1999

Does the uncertainty of commonly performed glucose measurements allow identification of individuals at high risk for diabetes?

Revised recommendations for diagnosis of diabetes introduce the intermediary risk group of impaired fasting glucose (IFG), defined as individuals with a fasting blood-glucose concentration between 5.6 and 6.0 mmol/l. We apply the concept of uncertainty to identifiable steps of sampling and measuring blood-glucose. Since many instruments in primary health care measure plasma-glucose and report results as blood-glucose and vice versa, factors affecting the transformation are also considered. The study identifies the measurement procedure as the major source of uncertainty, closely followed by preanalytical sources. The estimated uncertainties indicate that the presently available procedures do not allow identification of IFG by a single investigation. The approach to establish an uncertainty budget can be used to evaluate the clinical usefulness of measurements.

Blood Glucose↗
PubMed2004

Uncertainties and recommendations.

An assessment of the impacts of changes in climate and UV-B radiation on Arctic terrestrial ecosystems, made within the Arctic Climate Impacts Assessment (ACIA), highlighted the profound implications of projected warming in particular for future ecosystem services, biodiversity and feedbacks to climate. However, although our current understanding of ecological processes and changes driven by climate and UV-B is strong in some geographical areas and in some disciplines, it is weak in others. Even though recently the strength of our predictions has increased dramatically with increased research effort in the Arctic and the introduction of new technologies, our current understanding is still constrained by various uncertainties. The assessment is based on a range of approaches that each have uncertainties, and on data sets that are often far from complete. Uncertainties arise from methodologies and conceptual frameworks, from unpredictable surprises, from lack of validation of models, and from the use of particular scenarios, rather than predictions, of future greenhouse gas emissions and climates. Recommendations to reduce the uncertainties are wide-ranging and relate to all disciplines within the assessment. However, a repeated theme is the critical importance of achieving an adequate spatial and long-term coverage of experiments, observations and monitoring of environmental changes and their impacts throughout the sparsely populated and remote region that is the Arctic.

Animals↗
PubMed1975

Enhancement of conditioned reinforcement by uncertainty.

Pigeons were trained in three conditions. In the baseline condition, the birds responded on a fixed-interval schedule with the response key white. When the interval was completed, the key turned either red or green for a delay interval that was terminated by a grain presentation dependent on no key pecks during the final 2 sec. In the uncertainty condition, no grain was presented at the end of the delay periods when the key was red. In the certainty condition, the white light appeared only on occasions when pecking would turn the key green and produce food. Otherwise, the key was illuminated red throughout the total time period. The highest response rate in white occurred in the uncertainty condition, the next highest in the certainty condition, and the lowest in baseline. The results suggest that uncertainty facilitated responding, although uncertainty is not a necessary condition for conditioned reinforcement.

Journal Article↗
PubMedDate not supplied

Sensitivity and first-step uncertainty analyses for the preferential flow model MACRO.

Sensitivity analyses for the preferential flow model MACRO were carried out using one-at-a-time and Monte Carlo sampling approaches. Four different scenarios were generated by simulating leaching to depth of two hypothetical pesticides in a sandy loam and a more structured clay loam soil. Sensitivity of the model was assessed using the predictions for accumulated water percolated at a 1-m depth and accumulated pesticide losses in percolation. Results for simulated percolation were similar for the two soils. Predictions of water volumes percolated were found to be only marginally affected by changes in input parameters and the most influential parameter was the water content defining the boundary between micropores and macropores in this dual-porosity model. In contrast, predictions of pesticide losses were found to be dependent on the scenarios considered and to be significantly affected by variations in input parameters. In most scenarios, predictions for pesticide losses by MACRO were most influenced by parameters related to sorption and degradation. Under specific circumstances, pesticide losses can be largely affected by changes in hydrological properties of the soil. Since parameters were varied within ranges that approximated their uncertainty, a first-step assessment of uncertainty for the predictions of pesticide losses was possible. Large uncertainties in the predictions were reported, although these are likely to have been overestimated by considering a large number of input parameters in the exercise. It appears desirable that a probabilistic framework accounting for uncertainty is integrated into the estimation of pesticide exposure for regulatory purposes.

Adsorption↗
PubMedDate not supplied

Forecasting the number of soil samples required to reduce remediation cost uncertainty.

Sampling scheme design is an important step in the management of polluted sites. It largely controls the accuracy of remediation cost estimates. In practice, however, sampling is seldom designed to comply with a given level of remediation cost uncertainty. In this paper, we present a new technique that allows one to estimate of the number of samples that should be taken at a given stage of investigation to reach a forecasted level of accuracy. The uncertainty is expressed both in terms of volume of polluted soil and overall cost of remediation. This technique provides a flexible tool for decision makers to define the amount of investigation worth conducting from an environmental and financial perspective. The technique is based on nonlinear geostatistics (conditional simulations) to estimate the volume of soil that requires remediation and excavation and on a function allowing estimation of the total cost of remediation (including investigations). The geostatistical estimation accounts for support effect, information effect, and sampling errors. The cost calculation includes mainly investigation, excavation, remediation, and transportation. The application of the technique on a former smelting work site (lead pollution) demonstrates how the tool can be used. In this example, the forecasted volumetric uncertainty decreases rapidly for a relatively small number of samples (20-50) and then reaches a plateau (after 100 samples). The uncertainty related to the total remediation cost decreases while the expected total cost increases. Based on these forecasts, we show how a risk-prone decision maker would probably decide to take 50 additional samples while a risk-averse decision maker would take 100 samples.

Forecasting↗
PubMed2000

Handling uncertainty in cost-effectiveness models.

The use of modelling in economic evaluation is widespread, and it most often involves synthesising data from a number of sources. However, even when economic evaluations are conducted alongside clinical trials, some form of modelling is usually essential. The aim of this article is to review the handling of uncertainty in the cost-effectiveness results that are generated by the use of decision-analytic-type modelling. The modelling process is split into a number of stages: (i) a set of methods to be employed in a study are defined, which should include a 'reference case' of agreed methods to enhance the comparability of results; (ii) the clinical and demographic characteristics of the patients the model relates to should be specified as carefully as in any experimental study; and (iii) the data requirements of the model should be estimated using the principles of Bayesian statistics, such that prior distributions are specified for unknown model parameters. Monte Carlo simulation can then be employed to sample from these prior distributions to obtain a distribution of the cost effectiveness of the intervention. Such probabilistic analyses are related to parameter uncertainty. In addition, modelling uncertainty is likely to add a further layer of uncertainty to the results of particular analyses.

Cost-Benefit Analysis↗
PubMedDate not supplied

Uncertainty analysis in QUAL2E model of Zayandeh-Rood River.

Water-quality modeling and prediction is a complicated task because of inherent randomness and uncertainties associated with various processes and variables throughout the stream environment and the lack of appropriate data. Hence, the results of mathematical models are always approximate, lying within an uncertainty. This paper describes and demonstrates the application of the U.S. Environmental Protection Agency's water-quality model, QUAL2E-UNCAS, to the Zayandeh-Rood River in Iran. First-order reliability analysis is used to examine the variability of predicted water-quality parameters of total dissolved solids, dissolved oxygen, and biochemical oxygen demand. This analysis also determines key sources of uncertainty affecting prediction of the water-quality parameters. The results show that reliability analysis can help water-quality modelers and planners to quantify the reliability of the water-quality predictions and to carry out more efficiently planned sampling and data collection programs to reduce model-prediction uncertainty.

Forecasting↗
PubMedDate not supplied

Uncertainty of illness for persons with schizophrenia.

This qualitative research report presents an illustration of Mishel's (1990) reconceptualization of uncertainty in illness theory applied to persons with schizophrenia. The researcher interviewed 6 persons with schizophrenia and 5 family members. The informants reported being uncertain about whether their medicine would keep working, whether they would be able to provide for their children, whether they could stay on their medicine, whether their symptoms would improve, when the next relapse would be, and even whether they would survive. They appeared to be experiencing differing degrees of uncertainty and a variety of manifestations of probabilistic thinking. For some, uncertainty provided the opportunity for hope. For others, the uncertainty was perceived as a danger. For all of them, their view of life had changed.

Adult↗
PubMedDate not supplied

The representation of uncertainty in medical expert systems.

The development of the rule-based expert system has provided important new techniques for the representation of knowledge. However, continued use of this representational scheme has highlighted some of its deficiencies. In particular, many within scientific and non-scientific fields attempting to use the rule-base design to describe natural phenomena often find it difficult to represent the complexities of the world as 'absolute' rules. For this reason, many investigators acknowledge the need to add an uncertainty mechanism to the rule-base construct. Such a facility would allow the quantification of accuracy or strength of association within individual rules Although agreement exists on the need for an uncertainty representation facility, the debate concerning the most appropriate methodology is far from resolved. The purpose of this paper is to provide a review and commentary on the current state of debate over the five most popular candidate uncertainty models: symbolic representation, MYCIN certainty factors, Bayesian, Dempster-Shafer and fuzzy set logic. The advantages and disadvantages of each uncertainty calculi will be presented and assessed with respect to their applicability to the medical expert systems domain.

Bayes Theorem↗
PubMed1994

Contextual influences on interactive processing: effects of discriminability, quantity, and uncertainty.

Three contextual factors--(1) the discriminability of stimuli in pitch, (2) the number of stimuli differing in pitch, and (3) the uncertainty regarding which stimuli or tasks would appear--were manipulated as subjects performed speeded loudness classifications in each of six experiments. The magnitude of Garner interference and effects of congruity were used to gauge the degree of interactive processing. Enhancing pitch discriminability caused monotonic increases in interference and congruity. Stimulus-task uncertainty mediated the changes in Garner interference wrought by increased discriminability. Uncertainty also caused a surprising shift in congruity from strongly positive to strongly negative as uncertainty grew. Increasing stimulus quantity lowered interference, but had inconsistent effects on congruity. Regression analyses suggested that, collectively, these three contextual variables underlie most failures of selective attention in speeded classification.

Adult↗
PubMed1987

[Response uncertainty on rule learning by observation: effects of pre-experience on observational learning].

The present study was conducted to examine the hypothesis that children's feelings of uncertainty would mediate between pre-experience and rule acquisition in observational learning. After received a pretest, subjects were requested to estimate their response uncertainty concerning a task used in the pretest. Then they observed a model responding to a series of pictures each of which depicting one of four directions. The model's responses were governed by a rule consisted of two dimensions: the progression and the direction. After observing the demonstration, subjects received two post-tests which differed in the order of stimulus presentation and in terms of the reinforcement. Subjects enhancing their feelings of uncertainty in the pretest phase acquired a rule which contained a dimension of the progression, while subjects who did not enhance them acquired a rule used by the model. These findings were interpreted as generally supporting the hypothesis of response uncertainty as a mediator of rule learning.

Biofeedback, Psychology↗
PubMed1999

Set-up error & organ motion uncertainty: a review.

Conformal radiotherapy allows improvement in the treatment outcome due to increased targeting accuracy through advanced beam shaping techniques to precisely conform radiation dose to the geometry of the tumour. Treatment set-up and organ motion uncertainties are unavoidable factors that are limiting increases in accuracy and have to be accounted for in conformal treatment planning. The magnitudes of set-up errors and organ motion uncertainties for specific sites, and using various set-up techniques, have been quantified in the literature. However, the parameters used with these measurements and the presentation of the data has differed between studies for the same site. The purpose of this paper is to analyse and combine the published material into a uniform format and to display typical reported values of set-up and organ motion uncertainties. Values measured under similar conditions were averaged across studies. The results of this analysis illustrate (1) variability in the parameters used for measurements across studies, (2) typical motion ranges of the prostate, kidneys, liver and diaphragm, (3) typical means and standard deviations for set-up errors associated with the prostate, pelvis, brain, head and neck, thorax, rectum and breast and (4) a brief review of the common methods to lower or account for these uncertainties.

Brain↗
PubMedDate not supplied

Perioperative uncertainty and state anxiety of orthopaedic surgical patients.

PURPOSES: The purposes of this study were to determine (a) the relationship between preoperative uncertainty and anxiety of orthopaedic surgical patients in three adult developmental stages (young, middle, older) and (b) the differences in uncertainty and anxiety among the adult developmental stages, gender, and acuity levels of the disorder. DESIGN: Correlational and comparative with descriptive survey. SAMPLE: 106 adult orthopaedic surgical patients. METHODS: Subjects were contacted 1 to 2 weeks preoperatively during their preadmission visit or upon early admission the day of surgery. FINDINGS: All patients responded similarly in terms of having moderate levels of preoperative uncertainty and anxiety. There were no statistically significant differences among developmental stages, gender, or acuity levels for these orthopaedic patients. IMPLICATIONS FOR NURSING PRACTICE: Nurses need to be aware that adult orthopaedic patients such as these subjects may have moderate levels of uncertainty and anxiety prior to surgery. In addition to physical preparation for surgery, nurses need to help patients with their emotional concerns. The incorporation of preoperative psychoeducational interventions and improved communication into plans of care for all orthopaedic surgical patients is recommended.

Adolescent↗
PubMed1992

Quantitation of mapping uncertainty in Wolff-Parkinson-White syndrome. Implications for anatomic characterization and surgical division of accessory atrioventricular connections.

The purpose of this study was to quantitate the uncertainty inherent in the electrophysiologic mapping of ventricular preexcitation as seen in Wolff-Parkinson-White syndrome. An ink-coated needle electrode was constructed to serve as a point source of unipolar stimulation along the atrioventricular junction. Activation times for 11 ventricular mapping sites at the atrioventricular junction were measured for each stimulation point. Maps were successfully completed for 18 right free wall and 14 posterior septal stimulation points. The activation time at the mapping site closest to the stimulation point was termed the index activation time. Activation times identical to the index activation time were noted at 1.3 +/- 0.5 mapping sites for each free wall stimulation point and 1.9 +/- 0.9 mapping sites for each septal stimulation point (p < 0.05, septal versus free wall stimulation points). Activation times falling within 5 msec of the index activation time were noted at 2.4 +/- 1.0 mapping sites for each free wall stimulation point and at 3.9 +/- 1.4 mapping sites for each septal stimulation point (p < 0.05, septal versus free wall stimulation points). The uncertainty of electrophysiologic mapping can be quantitated, and this error should be considered when making inferences regarding the anatomy of accessory pathways based on electrophysiologic data. A knowledge of the uncertainty inherent in the localization of accessory atrioventricular connections by electrophysiologic mapping can be used to plan borders of surgical dissection that will account for this uncertainty at a 95% confidence level.

Animals↗
PubMedDate not supplied

The uncertainty (validity and reliability) of three electrothermometers in therapeutic modality research.

CONTEXT: Data from electrothermometers are used to determine therapeutic modality usage, but the value of experimental results is only as good as the data collected. OBJECTIVE: To determine the reliability and validity of 3 electrothermometers from 2 manufacturers. DESIGN: A 3 x 4 x 17 factorial with repeated measures on 2 factors. Independent variables were trial (1, 2, 3), thermometer (mercury thermometer, Iso-Thermex calibrated from -50 degrees C to 50 degrees C, Iso-Thermex calibrated from -20 degrees C to 80 degrees C, and Datalogger), and time (17). SETTING: Human Performance Research Center. INTERVENTION(S): Eighteen thermocouples were inserted through the wall of a foamed polystyrene cooler, and 6 were connected to each of the 3 electrothermometers. The cooler was positioned on a stir plate and filled with room-temperature water (18.4 degrees C). A mercury thermometer was immersed into the water bath. Measurements of the water bath were taken every 10 seconds for three 3-minute trials. MAIN OUTCOME MEASURE(S): The temperature variability of 3 electrothermometers was taken from a calibrated mercury thermometer. RESULTS: The Iso-Thermex electrothermometers did not differ statistically from each other in uncertainty (validity error +/- reliability error = 0.06 degrees C +/- 0.03 degrees C +/- 0.03 degrees C +/- 0.02 degrees C, P < .05), but both differed from the Datalogger (0.64 degrees C +/- 0.20 degrees C, P < .05). The Datalogger temperature was consistently higher than the mercury thermometer temperature. CONCLUSIONS: The Iso-Thermex electrothermometers were more stable than the Datalogger, and values were within the published uncertainty (+/-0.1 degrees C) when used with PT-6 thermocouples. The Datalogger we used had an uncertainty of measurement greater than that indicated in the user's manual (approximately +/-0.52 degrees C). Uncertainty of +/-0.84 degrees C can significantly influence the interpretation of results when intramuscular temperature changes are usually less than 5 degrees C.

Journal Article↗