Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Uncertainty”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 1,261 records · Page 70Linked to original sources
PubMedDate not supplied

Finalization of rule removes uncertainty.

Although the deadline for compliance with the Health Insurance Portability and Accountability Act Privacy Rule is only a few months away, some hospitals and other covered entities have essentially placed HIPAA compliance efforts on hold for the past several months because of the perceived uncertainty surrounding the rule's requirements. A new final rule was released on Aug. 9, removing this uncertainty and maintaining the April 14, 2003, deadline.

Confidentiality↗
PubMed1999

Dominant frequency uncertainty analysis of EEG alpha activity in pilots with transient ischemic attacks.

Objective. To study the characteristics of EEG after transient ischemic attack and to offer reference for screening procedure of aircrew and astronaut selection. Method. The dominant frequency uncertainty of alpha band EEG in 12 pilots (males; age 30 +/- 5) with transient ischemic episodes in middle cerebral artery (MCA) territories and in 20 normal healthy pilots was analyzed with frequency-fluctuation analysis. Result. The dominant probability of the main frequency coinciding with sites affected by transient ischemic attack (TIA) in patient pilots was higher than that in healthy pilots (P<0.01), and the dominant probability ratio logarithmic index I >or= 0 in all patient pilots with normal EEG, but I<0 in all healthy pilots. It was also found that not only I >or= 0, but the second component shifted to lower frequency (8 Hz) in patients with slight focal EEG alterations, i.e. slowing of frequency. The relative entropy values (percentage) were decreased significantly in pilots with TIA as compared with healthy pilots (P<0.05). Conclusion. The dominant frequency uncertainty analysis of alpha band showed clear superiority of computerized evaluation over routine visual assessment for the diagnosis of minor cerebral ischemia. It offers not only a possibility of studying pathophysiological functional parameter, but also the reference for screening procedure in aircrew and astronaut selection.

Acceleration↗
PubMed2003

[Knowledge of HIV/AIDS among urban adolescents: cultural consensus of doubts and uncertainties].

OBJECTIVE: To describe the knowledge of HIV/AIDS among adolescents from different socioeconomic strata (SS), using cultural consensus analysis. MATERIAL AND METHODS: A cross-sectional descriptive and analytic study was conducted from July 1995 to March 1996, among 758 adolescents from Guadalajara, México. Data were collected using a questionnaire, and analyzed by means of: a) consensus by SS and gender using factorial analysis; and b) identification of the cultural pattern of correct answers, and concordance of individual/group answers using Pearson's r correlation coefficients. RESULTS: There was a high degree of consensus across SS. The individual/group knowledge concordance was greater in higher SS. The pattern of correct responses showed: a) similar knowledge on casual transmission, AIDS characteristics, and higher risk in sex workers; and b) discrepancies regarding doubts and uncertainties about condom protection, distinction between HIV and AIDS, and HIV transmission in health clinics. CONCLUSIONS: Knowledge was homogeneous and mainly medically oriented across all SS. Nevertheless, there were elements of doubt and uncertainty that require differentiated informative interventions.

Adolescent↗
PubMed2002

[Parameters identification and uncertainty analysis for environmental model].

This paper examined a case study of hydrological model for identifying parameter uncertainty by using three sensitivity analysis methods: HSY algorithm, linear regressional method and coupling analysis method. The results showed that optimal algorithms cannot give a sound explanation for complexity of model structure and identifying model parameters via uncertainty analysis methods presented an effective alternative to understand model system.

Algorithms↗
PubMedDate not supplied

Perceived uncertainty, physical symptoms, and negative mood in hospitalized patients with chronic obstructive pulmonary disease.

OBJECTIVE: To determine whether perceived uncertainty and physical symptoms were related to negative mood in hospitalized patients with chronic bronchitis and/or emphysema. DESIGN: Descriptive correlational. SETTING: Five large teaching hospitals in a city in central Canada. SUBJECTS: The sample consisted of 15 men and 11 women ranging in age from 53 to 86 years. INSTRUMENTS: Mishel Uncertainty in Illness Scale; Somatic Scale of the Bronchitis Emphysema Symptom Checklist; and Tension, Depression and Anger Subscales of the Profile of Mood States. RESULTS: Only the variable of physical symptoms contributed to the negative mood of the subjects with chronic obstructive pulmonary disease, explaining 21% of the variance (p < 0.02). Of the four symptom categories measured (fatigue, dyspnea, congestion, and peripheral-sensory disturbance), only fatigue was a significant predictor (p < 0.006) of negative mood, accounting for 28% of the variance. CONCLUSION: Negative mood is evidence of impaired coping. The finding that fatigue contributed to negative mood provides support for the theoretic prediction that low energy interferes with an individual's ability to cope with a stressful situation.

Adaptation, Psychological↗
PubMed2003

[Efficiency of a visual system under conditions of uncertainty of the appearance of a moving object].

The effect of uncertainty of a moving object appearance in the noise field upon the coefficient efficiency, we studied. At short durations of presentation (40-80 msec) and high level of external noise, this effect was maximal: magnified 100 times. The efficiency coefficient dependence on the duration of a moving object presentation was shown to be characterized by two maximums. The position of minimum situated between these two maximums was found to be independent of either presence or absence of uncertainty of a number of parameters: such as initial position of the object the image, time of its appearance, noise level, velocity and direction of the movement, and has a latency approximately 120 sec. A functional model of the observed phenomena, has been proposed.

Humans↗
PubMed2003

Uncertainties regarding dengue modeling in Rio de Janeiro, Brazil.

Dengue fever is currently the most important arthropod-borne viral disease in Brazil. Mathematical modeling of disease dynamics is a very useful tool for the evaluation of control measures. To be used in decision-making, however, a mathematical model must be carefully parameterized and validated with epidemiological and entomological data. In this work, we developed a simple dengue model to answer three questions: (i) which parameters are worth pursuing in the field in order to develop a dengue transmission model for Brazilian cities; (ii) how vector density spatial heterogeneity influences control efforts; (iii) with a degree of uncertainty, what is the invasion potential of dengue virus type 4 (DEN-4) in Rio de Janeiro city. Our model consists of an expression for the basic reproductive number (R0) that incorporates vector density spatial heterogeneity. To deal with the uncertainty regarding parameter values, we parameterized the model using a priori probability density functions covering a range of plausible values for each parameter. Using the Latin Hypercube Sampling procedure, values for the parameters were generated. We conclude that, even in the presence of vector spatial heterogeneity, the two most important entomological parameters to be estimated in the field are the mortality rate and the extrinsic incubation period. The spatial heterogeneity of the vector population increases the risk of epidemics and makes the control strategies more complex. At last, we conclude that Rio de Janeiro is at risk of a DEN-4 invasion. Finally, we stress the point that epidemiologists, mathematicians, and entomologists need to interact more to find better approaches to the measuring and interpretation of the transmission dynamics of arthropod-borne diseases.

Aedes↗
PubMedDate not supplied

Uncertainties in physical and biological targeting with radiation therapy.

Advances in radiation therapy over the past decade have resulted from increased accuracy of imaging and highly conformal three dimensional treatment planning and delivery of radiation therapy. Three-dimensional conformal radiation therapy (3D CRT) with higher doses than previously considered tolerable is now standard for many types of cancer. Intensity modulated radiation therapy (IMRT) with x-rays, proton beam treatments and intensity modulated proton therapy (IMPT) are major areas of research. Tumor motion between and even during radiation treatments represents a major uncertainty. Tumor heterogeneity results in additional uncertainties affecting tumor control with radiation therapy. Imaging the heterogeneous targets within tumors offers new opportunities for tumor delineation. Molecular therapeutic agents enhance the effects of ionizing radiations in murine systems. Clinical trials combining molecular targeting agents with conformal radiation therapy are being initiated.

Animals↗
PubMed2004

TSS concentration in sewers estimated from turbidity measurements by means of linear regression accounting for uncertainties in both variables.

In order to replace traditional sampling and analysis techniques, turbidimeters can be used to estimate TSS concentration in sewers, by means of sensor and site specific empirical equations established by linear regression of on-site turbidity Tvalues with TSS concentrations C measured in corresponding samples. As the ordinary least-squares method is not able to account for measurement uncertainties in both T and C variables, an appropriate regression method is used to solve this difficulty and to evaluate correctly the uncertainty in TSS concentrations estimated from measured turbidity. The regression method is described, including detailed calculations of variances and covariance in the regression parameters. An example of application is given for a calibrated turbidimeter used in a combined sewer system, with data collected during three dry weather days. In order to show how the established regression could be used, an independent 24 hours long dry weather turbidity data series recorded at 2 min time interval is used, transformed into estimated TSS concentrations, and compared to TSS concentrations measured in samples. The comparison appears as satisfactory and suggests that turbidity measurements could replace traditional samples. Further developments, including wet weather periods and other types of sensors, are suggested.

Calibration↗
PubMed2005

Impact of dimension uncertainty and model calibration on sewer system assessment.

Assessments of sewer performance are usually based on a single computation of CSO (combined sewer overflow) volumes using a time series of rainfall as system loads. A shortcoming of this method is that uncertainties in knowledge of sewer system dimensions are not taken into account. Moreover, sewer models are rarely calibrated. This paper presents the impacts of database errors and model calibration on return periods of calculated CSO volumes. The impact of uncertainties is illustrated with two examples. Variability of calculated CSO volumes is estimated using Monte Carlo simulations. The results show that calculated CSO volumes vary considerably due to database errors, especially uncertain dimensions of the catchment area. Furthermore, event-based calibration of a sewer model does not result in more reliable predictions because the calibrated parameters have low portability. However, it enables removal of database errors harmonising model predictions and 'reality'.

Calibration↗
PubMed2005

The nitrogen cycle, scientific uncertainty and policy relevant science.

Much of the research on the nitrogen cycle aims to improving scientific understanding but is not focused specifically on removing or reducing the scientific uncertainties that constrain policy makers in the formulation of appropriate responses to old or emerging environmental problems. Policy makers, for example, commonly find it difficult to assess the spatial or temporal importance of the various risks to human and ecosystem health that stem from man's interference with the natural N cycle. This paper will justify this conclusion by reference to the findings of a recent study on non-point pollution from crop production in China. The findings concern the perceived risks of groundwater nitrate to human health; uncertainties about critical NOx levels and their interactions with other pollutants; various other dimensions of man's impact on the N cycle. The paper will go on to suggest a more systematic process or pathway by which scientists can select and design their research in a manner that could give more effective support to policy makers.

China↗
PubMed2006

Uncertainties in sediment erodibility estimates due to a lack of standards for experimental protocols and data interpretation.

Quantitative prediction of the erodibility of muds and mud-sand mixtures is, at present, seldom possible without resorting to direct measurements, preferably in situ. A variety of devices and protocols have been developed for erosion testing, but a considerable degree of uncertainty remains with regard to the accuracy and comparability of the resulting data. This paper argues that differences in experimental protocols and data analysis procedures are a major contributing factor to uncertainty in estimates of sediment erodibility. In particular, the likelihood of a time-dependent erosion rate response under typical erosion testing conditions means that the time history of applied forcing and the chosen protocols for analyzing and interpreting data directly affect derived erosion parameters. Several straightforward ways to address this problem are suggested, including standardization of experimental design and data analysis protocols, explicit recognition and adoption of appropriate erosion model(s), and allowing for potential time/depth changes in erodibility. Experimentalists should also archive and share erosion-test time series, not just derived parameters, so that data sets may be reanalyzed within a different framework if necessary. An example is presented from an intercomparison experiment between the Virginia Institute of Marine Sciences Sea Carousel and the University of Maryland Center for Environmental Science Microcosm System, carried out in the upper Chesapeake Bay (Maryland, USA) in May 2002. Derived parameters appear to be incompatible when the data are analyzed using different procedures, but real similarities and differences are readily apparent when the data are analyzed using the same procedures.

Conservation of Natural Resources↗
PubMedDate not supplied

Sampling almonds for aflatoxin, part I: estimation of uncertainty associated with sampling, sample preparation, and analysis.

Domestic and international regulatory limits have been established for aflatoxin in almonds and other tree nuts. It is difficult to obtain an accurate and precise estimate of the true aflatoxin concentration in a bulk lot because of the uncertainty associated with the sampling, sample preparation, and analytical steps of the aflatoxin test procedure. To evaluate the performance of aflatoxin sampling plans, the uncertainty associated with sampling lots of shelled almonds for aflatoxin was investigated. Twenty lots of shelled almonds were sampled for aflatoxin contamination. The total variance associated with measuring B1 and total aflatoxins in bulk almond lots was estimated and partitioned into sampling, sample preparation, and analytical variance components. All variances were found to increase with an increase in aflatoxin concentration (both B1 and total). By using regression analysis, mathematical expressions were developed to predict the relationship between each variance component (total, sampling, sample preparation, and analysis variances) and aflatoxin concentration. Variance estimates were the same for B1 and total aflatoxins. The mathematical relationships can be used to estimate each variance for a given sample size, subsample size, and number of analyses other than that measured in the study. When a lot with total aflatoxins at 15 ng/g was tested by using a 10 kg sample, a vertical cutter mixer type of mill, a 100 g subsample, and high-performance liquid chromatography analysis, the sampling, sample preparation, analytical, and total variances (coefficient of variation, CV) were 394.7 (CV, 132.4%), 14.7 (CV, 25.5%), 0.8 (CV, 6.1%), and 410.2 (CV, 135.0%), respectively. The percentages of the total variance associated with sampling, sample preparation, and analytical steps were 96.2, 3.6, and 0.2, respectively.

Aflatoxin B1↗
PubMed1989

[Uncertainties in the localization of radiation sources in brachytherapy].

While investigating ways to solve the problem of locating radiation sources applied in brachytherapy a device was constructed which enables a precise assessment of their or their applicators' position from two only roughly positioned orthogonal radiographs. The overall accuracy (including exposure and evaluation) achieved is +/- 1 mm. The constructional elements and the evaluation algorithm are described and the influence of the location uncertainty on the uncertainty of the dose applied are discussed.

Algorithms↗
PubMed1988

Does impaired contrast sensitivity explain the spatial uncertainty of amblyopes?

We investigated the possibility that the spatial imprecision of amblyopic eyes can be accounted for by the relative insensitivity to contrast that has been documented for these eyes. Thresholds for the discrimination of spatial misalignment, a measure of spatial uncertainty, were determined for three amblyopes and one normal for targets ranging in contrast from detection threshold to 99%. We found that spatial uncertainty was greater in amblyopic eyes than non-amblyopic eyes for targets equally above contrast threshold, and when the targets were presented at threshold contrast to the nonamblyopic eyes and at 99% contrast to the amblyopic eyes. Our results fail to support the possibility that the spatial imprecision of amblyopic eyes can, in general, be attributed to reduced contrast sensitivity. Different neural abnormalities are presumed to limit amblyopes' performance on different spatial tasks.

Amblyopia↗
PubMed1986

[Principle of uncertainty in vision].

When investigating the dependence of the bandwidth of the spatial frequency characteristic (delta F) of the receptive fields of the cat striate cortex on the size (D) of the receptive field it was shown that delta FD = 1.2. Thus in the system of elements performing the processing of information in the visual cortex the inaccuracy of the signal representation in the spatial frequency and in space is related by an uncertainty principle. The size of the constant evidences that the weighting functions of elements are sinusoids or cosinusoids modulated by squarewave impulse rather than by the Gabor elements. The performing of uncertainty principle and the size of the constant are arguments in favour of the hypothesis that the receptive fields of the visual cortex organize a quasilinear basis.

Animals↗
PubMed1980

The evolution of medical uncertainty.

Modern developments of scientific medicine have uncovered and created uncertainties and risks that were previously not known or experienced; the stakes have become very much higher. The rise in public expectation, however, is paralleled by a lowered tolerance of uncertainty. Metaphors of "deliverance" and "disaster" abound in discussions of scientific discovery, reflecting differing conceptions and philosophies about errors and mistakes, and the role they play in the physical universe, the biosphere, and human affairs. These concerns highlight the difficulties and dilemmas of finding scientifically adequate, culturally appropriate, and socially effective ways of appraising and controlling risk.

Adult↗
PubMed1982

The effect of movement uncertainty on reaction and movement times of learning disabled and normal boys.

This study examined the effect of potential stimuli, as a source of movement uncertainty, on the reaction time (RT) and movement time (MT) of learning disabled (LD) children during a simple running task. The ability of LD children to attend to a process stimuli is known to be inferior. Such a notion is relevant to motor skill development as it imposes on the child's ability to develop from movement consistencies to movement constancies. When confronted with movement uncertainty, LD children showed significant increases in RT and MT over a 4.6 m. run. The performance of normal controls remained constant, thus emphasizing the simplicity of the task. The importance of skill consistency was highlighted, as was the consideration of inferior psychological processes of LD children while implementing movement activities.

Child↗