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PubMed2006

An uncertainty analysis of the flood-stage upstream from a bridge.

The paper begins with the formulation of the problem in the form of a general performance function. Next the Latin hypercube sampling (LHS) technique--a modified version of the Monte Carlo method is briefly described. The essential uncertainty analysis of the flood-stage upstream from a bridge starts with a description of the hydraulic model. This model concept is based on the HEC-RAS model developed for subcritical flow under a bridge without piers in which the energy equation is applied. The next section contains the characteristic of the basic variables including a specification of their statistics (means and variances). Next the problem of correlated variables is discussed and assumptions concerning correlation among basic variables are formulated. The analysis of results is based on LHS ranking lists obtained from the computer package UNCSAM. Results fot two examples are given: one for independent and the other for correlated variables.

Disasters↗
PubMed2005

Assisted living: a place to manage uncertainty. The ambiguity of assisted living is unavoidable because residents' needs are always changing. The Wheat Valley example is used to examine this concept.

The assisted living environment lacks the satisfying clarity of the consumer model (a stay at the Holiday Inn) or the medical model (the hospital or nursing home). Yet the ambiguity of assisted living is unavoidable because it shelters individuals whose needs are changing, the model of care requires extensive negotiation with residents, and staff members must continually compromise as they implement the principles. Assisted living is a place where uncertainty is managed, not resolved. This indicates a need for the further pursuit of qualitative research, such as reported by these articles and others (e.g., Carder, 2002), to explore how participants construct, make sense of, and interpret their daily experience in assisted living.

Activities of Daily Living↗
PubMed2004

Genome wide expression profiling of angiogenic signaling and the Heisenberg uncertainty principle.

Genome wide DNA expression profiling coupled with antibody array experiments using endostatin to probe the angiogenic signaling network in human endothelial cells were performed. The results reveal constraints on the measuring process that are of a similar kind as those implied by the uncertainty principle of quantum mechanics as described by Werner Heisenberg. We describe this analogy and argue for its heuristic utility in the conceptualization of angiogenesis as an important step in tumor formation.

Angiogenesis Inhibitors↗
PubMed1988

Dealing with uncertainty, risks, and tradeoffs in clinical decisions. A cognitive science approach.

To generate hypotheses about how physicians make difficult clinical decisions, we analyzed transcripts of the "thinking aloud" behavior of expert clinicians making a testing or treatment decision with an uncertain diagnosis. We compared the clinicians' reasoning with a decision analysis of the same problem. The experts did not formulate a global outline of their decision, but chained together a sequence of decisions based on available and incomplete information. Despite effective and efficient problem solving, the clinicians used numeric terms only as symbolic representations of likelihood, used limited information in choosing among alternatives, and dismissed the possibility that a less conventional strategy, empiric therapy, might yield equivalent outcome. We describe cognitive problem-solving strategies and knowledge representations that permit persons to make successful decisions despite limited processing resources. The same cognitive procedures probably contribute to observed errors in decision-making under uncertainty.

Amphotericin B↗
PubMedDate not supplied

Uncertainty of analytical determinations.

Two examples of uncertainty calculation are described for determination of nitrates in solution (APHA method 4500B) and total suspended solids in water (APHA method 2540D).

Mathematics↗
PubMedDate not supplied

Uncertainty in most probable number calculations for microbiological assays.

Microbiological assays commonly use incubations of multiple tubes in a dilution series, and microorganism concentration is read as a most probable number (MPN) in standard tables for the observed pattern of positive tubes. Published MPN tables differ, sometimes substantially, because of use of approximate MPN calculation procedures, different rounding conventions in the results, and different methods of calculating confidence or credible intervals. We conclude that the first 2 issues can now be resolved by using recently developed exact MPN calculation methods and by reporting rounding conventions in standard tables. The third issue is not amenable to complete resolution, especially if credible interval (as opposed to confidence interval) limits are desired--as we think they most often are. In that case, Bayesian statistics are called for and the analyst must provide a distribution of concentration that was presumed to be true before the assay was performed. This is mathematically combined with the assay data, resulting in a posterior concentration distribution. These distributions may then be used to quantify the uncertainty in the MPN estimate, and the best approach is to use the highest posterior density regions of these distributions. If based on diffuse prior information (positing that, prior to an assay being performed, all positive concentrations are equally likely), then established procedures might be used to calculate the limits and publish them in standard tables. In the event that this prior assumption is held to be not satisfactory, we show results for an empirical Bayes procedure, with a Poisson prior distribution, giving credible interval widths much narrower than in the other cases examined.

Bayes Theorem↗
PubMed2004

[Cost-utility analysis; uncertainties restrict applicability].

Assumptions and choices are inherent to cost-utility analysis, the economic technique that provides a generic measure for the quantification of the efficiency of various health-care services. Uncertainty prevails on many of them: on the definition of the output of health care as health gain, on its expression in quality-adjusted life years (QALYs), on the choice of measurement instruments that should provide comparable information across all disease categories, on the choice of the procedure to value health states, on the relative importance of the judgments of patients and the general public, on the quantification of various types of costs, and on the question as to whether, and then how, future health gains should be discounted. The conclusion is that the results of a cost-utility analysis should be interpreted with caution. For the time being, cost-utility analysis cannot be used for direct comparisons of efficiency across all types of health-care services.

Attitude to Health↗
PubMed2005

A benchmark methodology for managing uncertainties in urban runoff quality models.

In this paper we present a benchmarking methodology, which aims at comparing urban runoff quality models, based on the Bayesian theory. After choosing the different configurations of models to be tested, this methodology uses the Metropolis algorithm, a general MCMC sampling method, to estimate the posterior distributions of the models' parameters. The analysis of these posterior distributions allows a quantitative assessment of the parameters' uncertainties and their interaction structure, and provides information about the sensitivity of the probability distribution of the model output to parameters. The effectiveness and efficiency of this methodology are illustrated in the context of 4 configurations of pollutants' accumulation/erosion models, tested on 4 street subcatchments. Calibration results demonstrate that the Metropolis algorithm produces reliable inferences of parameters thus, helping on the improvement of the mathematical concept of model equations.

Algorithms↗
PubMed2005

Incorporating uncertainty into predictions of diffuse-source phosphorus transfers (using readily available data).

Phosphorus (P) is a limiting nutrient in many freshwater ecosystems and increases in its availability can lead to eutrophication. Effective management of P in freshwaters requires quantitative estimates of P supply from all significant sources. A simple GIS-based model, capable of predicting total diffuse source phosphorus export from catchments using readily available data, has been developed. The model is based on the idea of export coefficients but includes the effects of topography (slope and cumulative area), soil type (using the U.K. Hydrology of Soil Types (HOST) classification) and climate (hydrologically effective rainfall) as well as land use. Uncertainty in key model parameters is accounted for using Monte Carlo simulation which involves random sampling from probability density functions in a large number of iterations. This reduces the need for subjective optimisation of export coefficients. The model has been applied to the Greens Burn catchment, Scotland and predicts P exports within the confidence limits of the measured values.

Geographic Information Systems↗
PubMed2005

The precautionary principle and international conflict over domestic regulation: mitigating uncertainty and improving adaptive capacity.

Disputes over invocation of precaution in the presence of uncertainty are building. This essay finds: (1) analysis of past WTO panel decisions and current EU-US regulatory conflicts suggests that appeals to scientific risk assessment will not resolve emerging conflicts; (2) Bayesian updating strategies, with commitments to modify policies as information emerges, may ameliorate conflicts over precaution in environmental and security affairs.

Commerce↗
PubMed2006

[Harmonisation of validation strategies and estimation of the associated uncertainty in the framework of assay laboratoires accreditation].

In order to achieve the harmonization of validation strategies, the interpretation of several validation criteria is proposed. Furthermore, a simple and visual decision tool to assess the validity of an analytical procedure is described: the accuracy profile based on the estimation of the total error of the measurements. This profile build with beta-expectation tolerance intervals can also compute with efficiency the uncertainty related to the results of a laboratory, which is an essential parameter for the accreditation of laboratories under ISO 17025.

Accreditation↗
PubMed1985

Physician tolerance for uncertainty. Use of liver-spleen scans to detect metastases.

To gain insight into diagnostic test use, we interviewed 42 physicians who ordered 62 liver-spleen scans to detect possible metastases. Before receiving the actual scan results, physicians gave (1) pretest probability estimates for liver metastasis; (2) probability estimates and management plans given the most common scan results; and (3) probabilities above and below which they would stop the diagnostic workup (their decision thresholds). After learning the actual scan results, physicians gave their posttest probabilities and management plans. Thirteen physicians (31%) desired absolute certainty to rule in metastasis. Fifty percent planned further evaluations even when probability estimates of metastasis reached one of their probability targets for ending the workup. Greater attention to decision thresholds may improve physicians' understanding of their tolerance for diagnostic uncertainty and the ability of diagnostic tests to reduce it.

Attitude of Health Personnel↗
PubMed1996

Regret graphs, diagnostic uncertainty and Youden's Index.

Regret is the difference in outcome between the action we took and the best action we could, in retrospect, have taken. 'Tent graphs', representing decision problems under uncertainty in terms of expected regret, offer an instructive geometric supplement to standard formulae, allow instant calculations, and suggest, as we shall illustrate, novel algebraic properties. For instance, the problem of finding the pre-test probability range in which it is worthwhile doing a diagnostic test becomes trivial, even when test costs depend on the unknown disease status; we take the opportunity to explore the (non-trivial) algebraic properties of this problem. The graphs also provide a simple way to illustrate and read off the expected value of information and expected value of perfect information. This property is used to derive a clinical interpretation of Youden's Index (sensitivity + specificity - 1), namely, it is the maximum proportional reduction in expected regret achieved by the test. Finally, we examine the relationship between Youden's Index and the area under an ROC curve.

Aged↗
PubMed1977

Prior time uncertainty reduction of foreperiod duration in schizophrenia and old age.

Four groups of college students, alcoholics, schizophrenics, and old age Ss judged stimulus durations of .50 and .55 seconds. The stimulus was preceded by a sound that functioned as the warning signal. The foreperiod duration, that is, the interval between the onsets of the warning signal and the stimulus, was variable and was either 1,3, or 5 seconds. There was no group difference with respect to the effect of foreperiod variability. Estimation of stimulus duration was a monotonically increasing function of foreperiod duration. However, when pitch of the sound was correlated with the corresponding foreperiod duration, this monotonic relation between foreperiod duration and estimation of stimulus duration was eliminated for schizophrenics, but not for nonschizophrenics. Although schizophrenics were not distinguishable from nonschizophrenics in terms of the effect of foreperiod variability, receptivity to prior information associated with time uncertainty reduction was shown to be unique for schizophrenia.

Acoustic Stimulation↗
PubMed1999

A preliminary statistical examination of the effects of uncertainty and variability on environmental regulatory criteria for ozone.

Basing the quantitative expression of environmental regulatory standards and associated compliance criteria on statistical principles has recently received attention in Europe, most visibly in a study by the UK Royal Commission on Environmental Pollution. These issues are timely for consideration in the USA, where a recent periodic review of National Ambient Air Quality Standards (NAAQS) has led to revision of the regulatory standards for ambient ozone and particulate matter. Salient statistical issues include accounting for errors of the first and second kind due to sampling and measurement error. These issues appear routine statistically and also may seem absent from regulations, but neither is necessarily the case. This paper is directed towards developing a methodology for examining the problem of dealing with uncertainty and variation in environmental regulations and compliance criteria. Our approach is illustrated through statistical analysis of the (old) 1 hour and the (new) 8 hour standards for ambient ozone, based on intensive monitoring in California's San Joaquin Valley during summer 1990 performed under the SARMAP Project. This paper presents preliminary findings based on quantifying measurement error or precision in terms of small-scale spatial and temporal variability, laying the groundwork for future work.

Air Pollutants↗
PubMed1988

Evaluating the uncertainty of risk prediction in genetic counseling: a Bayesian approach.

A general method to obtain the exact point estimate and the measure of uncertainty of recurrence risks for genetic counseling is present. This method, which follows Bayesian estimation theory, can be applied without restrictions of sample size, class of risk function, or parameter dimension. As an illustration, the recurrence risks for isolated cases in two autosomal dominant disorders with incomplete penetrance (mandibulofacial and fontonasal dyostoses) are estimated.

Bayes Theorem↗
PubMed2006

A computer-aided approach to compare the production economics of fed-batch and perfusion culture under uncertainty.

Fed-batch and perfusion culture dominate mammalian cell culture production processes. In this paper, a decision-support tool was employed to evaluate the economic feasibility of both culture modes via a case study based upon the large-scale production of monoclonal antibodies. The trade-offs between the relative simplicity but higher start-up costs of fed-batch processes and the high productivity but higher chances of equipment failure of perfusion processes were analysed. Deterministic analysis showed that whilst there was an insignificant difference (3%) between the cost of goods per gram (COG/g) values, the perfusion option benefited from a 42% reduction in capital investment and a 12% higher projected net present value (NPV). When Monte Carlo simulations were used to account for uncertainties in titre and yield, as well as the risks of contamination and filter fouling, the frequency distributions for the output metrics revealed that neither process route offered the best of both NPV or product output. A product output criterion was formulated and the options that met the criterion were compared based on their reward/risk ratio. The perfusion option was no longer feasible as it failed to meet the product output criterion and the fed-batch option had a 100% higher reward/risk ratio. The tool indicated that in this particular case, the probabilities of contamination and fouling in the perfusion option need to be reduced from 10% to 3% for this option to have the higher reward/risk ratio. The case study highlighted the limitations of relying on deterministic analysis alone.

Antibodies, Monoclonal↗