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PubMed2001

A proficiency testing scheme for aromatic hydrocarbons in air by the manual thermal desorption-GC method: a comparison of laboratory performance with the uncertainty requirements of the European Union Ambient Air Directive.

The Workplace Analysis Scheme for Proficiency (WASP) is a proficiency testing scheme for the analysis of occupational hygiene and environmental air samples and is operated in the UK by the Health and Safety Laboratory. Since 1997, WASP has offered samples of benzene, toluene and m-xylene, at environmental levels on Tenax, and has about 35 laboratories participating, mostly from industry, local government and consultancy organisations in the UK. The results reported cover the first 10 rounds of the environmental analytes (1997-1999) and demonstrate the important role of proficiency testing in assessing the quality of laboratory performance. Estimates are obtained for within-laboratory precision and the total variability at each analyte level. The estimates of within-laboratory precision suggest that laboratories have more difficulty analysing toluene and m-xylene than benzene. Linear relationships for the reproducibility relative standard deviation (RSDT) with loading level are evident for the analytes at occupational levels. At environmental levels, the relationship between loading level and reproducibility is much less well defined. The standard deviation for the proficiency testing assessment for all three analytes at the environmental level is 14%, as derived from the benzene data. Expanded uncertainty estimates (k = 1.96), for the analysis of samples since the scheme started, are obtained from the average total variance, and are 27% for benzene, 39% for toluene and 36% for m-xylene. Although the linear trend of performance against round number was not significant at the 95% level of confidence (p = 0.23 for benzene, p = 0.3 for toluene and p = 0.32 for m-xylene), there was a general improvement in RSDT from 26-34% to about 8-13% 10 rounds later. Currently, for a laboratory to meet one of the data quality objectives in the Ambient Air Directive (indicative measurement of benzene, expanded uncertainty +/- 30% or less), it would have to achieve a level of analytical performance to satisfy the category 1 (best performance) limit of better than +/- 8.8%. In the last proficiency testing round, discussed in this paper, only 58% of laboratories obtained performance scores that indicated that they were able to consistently achieve this level of performance.

Air Pollutants↗

PubMed2002

The purity of laboratory chemicals with regard to measurement uncertainty.

The purity P of laboratory chemicals is often declared in the form P > or = xy% (e.g., P > or = 97%). With a randomly chosen set of 40 compounds we found that their purity is generally closer to 100% than to the lower limit. The distribution of the purity data as found in the laboratory depends on the analytical technique used. Whereas purities determined by chromatography do not exceed 100% (because the sum of all observed peak areas is set to 100%), the purities obtained by titration can exceed 100% (because the functionality of the compound is measured). Therefore, the data for these two groups need to be dealt with in different ways. For purities based on titration we propose to use a rectangular distribution with a range from Pmin to 101%, an expected purity value which is the mean and a standard uncertainty of the purity u(P) of 29% of the range. Purities determined by chromatography can be described with a triangular distribution (ramp function). One leg of the triangle represents the range from Pmin to 100% and the right-angle is located at 100%. The expected value is the median and the uncertainty u(P) is 24% of the range. These proposals match the experimental data well.

Journal Article↗

PubMed2006

Reporting measurement uncertainty and coverage intervals near natural limits.

Different methods of treating data which lie close to a natural limit in a feasible range, such as zero or 100% mass or mole fraction, are discussed and recommendations made concerning the most appropriate. The methods considered include discarding observations beyond the limit, shifting observations to the limit, truncation of a classical confidence interval based on Student's t (coupled with shifting the result to the limit if outside the feasible range), truncation and renormalisation of an assumed normal distribution, and the maximum density interval of a Bayesian estimate based on a normal measurement distribution and a uniform prior within the feasible range. Based on consideration of bias and simulation to assess coverage, it is recommended that for most purposes, a confidence interval near a natural limit should be constructed by first calculating the usual confidence interval based on Student's t, then truncating the out-of-range portion to leave an asymmetric interval and adjusting the reported value to within the resulting interval if required. It is suggested that the original standard uncertainty is retained for uncertainty propagation purposes.

Journal Article↗

PubMed1979

Effects of listener uncertainty on articulatory inconsistency.

This investigation determined the effects of listener uncertainty on articulatory inconsistency. Subjects were 15 children between three and five years of age. Each subject was tested to find a set of 45 pictures to which articulatory responses would contain sound errors on: /f,v,th,s,ts,dz/. After one week, articulatory responses to these 45 stimuli elicited by traditional picture naming techniques were compared to productions of the same words elicited in an experimental communication setting. The number of sound errors decreased significantly (p less than or equal to 0.01) in the experimental communication setting when the listener pretended to be uncertain of what the speaker said. This finding was interpreted to mean that listener uncertainty may increase the effectiveness of articulatory remediation procedures if included in treatment programs.

Articulation Disorders↗

PubMed2001

Mitotic counting in surgical pathology: sampling bias, heterogeneity and statistical uncertainty.

Mitotic counting in surgical pathology: sampling bias, heterogeneity and statistical uncertainty Although several articles on the methodological aspects of mitotic counting have been published, the effects of macroscopic sampling and tumour heterogeneity have not been discussed in any detail. In this review the essential elements for a standardized mitotic counting protocol are described, including microscopic calibration, specific morphological criteria, macroscopic selection, counting procedure, effect of biological variation, threshold, and the setting of an area of uncertainty ('grey area'). We propose that the use of a standard area for mitotic quantification and of a grey area in mitotic counting protocols will facilitate the application of mitotic counting in diagnostic and prognostic pathology.

Data Interpretation, Statistical↗

PubMed1998

Facing uncertainty and possible death: the Christian patients' experience.

This paper presents the hospital experience of a group of coronary artery bypass graft surgery patients. A description of the qualitative methodology is given. The participants' experience was identified as facing uncertainty and possible death. Excerpts from interviews are given. The participants coped with the situation by praying or having others pray on their behalf. Their uncertainty and possible death was affected by the conditions of: available support; environment; credible authority; information; belief; and their psychophysiological status at the time.

Adaptation, Psychological↗

PubMed2002

"Nothing is carved in stone!": uncertainty in children with cancer and their families.

Although more children are surviving childhood cancer, they and their families still face many new stressors and challenges. Understanding the experiences of childhood cancer in children and families is conditional upon building a sound and comprehensive knowledge base that is grounded in research. Accordingly, a longitudinal interpretive qualitative study was conducted to arrive at an understanding of children's and families' perspectives on having to experience the childhood cancer-symptom trajectory. A purposive sample of 39 children with cancer and their families were recruited into the study. Open-ended interviews and participant observation were the primary data collection methods. Data were analyzed by the constant comparative method of grounded theory and analysis of illness narratives. Findings revealed that in addition to the stress and suffering resulting from the children's multiple symptom experiences, children and their families experienced many other events or 'rough spots' that made cancer and life difficult to get through. Although the 'rough spots' were numerous and varied, they all resulted in children and their families experiencing feelings of uncertainty. This paper focuses on describing the nature of uncertainty experienced by the children with cancer and their families. Recommendations for nursing practice and research are discussed.

Journal Article↗

PubMed2000

Uncertainty of the electrocardiogram: old and new ideas for assessment and interpretation.

The electrocardiogram (ECG) is a highly complex, dynamic and stochastic phenomenon. Although it provides a valuable, noninvasive and rapid means of assessing cardiac state and its change, uncertainties in its measurement and variation in the underlying electrophysiology that generates the ECG make difficult further improvement in its reliability for detecting and monitoring cardiac pathologies and conditions. This article reviews the sources of variability and uncertainty in ECG measurement and interpretation, revisits some old ideas for dealing with them, and proposes some novel directions for improving accuracy of ECG assessment and interpretation. We shall explore relative information content of lead systems, representation of ECG signals and patterns, and estimation of ECG distributions from limited lead systems. In addition, we will compare strategies for measuring ECG information and suggest new paradigms for feature extraction that reduce the sensitivity of assessment accuracy to intrinsic and extrinsic measurement errors. Finally, we review the importance of including dynamic information in ECG assessment, both for interpreting current cardiac state as well as for monitoring its change and significance.

Electrocardiography↗

PubMed2005

Nondivergent classical response functions from uncertainty principle: quasiperiodic systems.

Time-divergence in linear and nonlinear classical response functions can be removed by taking a phase-space average within the quantized uncertainty volume O(hn) around the microcanonical energy surface. For a quasiperiodic system, the replacement of the microcanonical distribution density in the classical response function with the quantized uniform distribution density results in agreement of quantum and classical expressions through Heisenberg's correspondence principle: each matrix element (u/alpha(t)/v) corresponds to the (u-v)th Fourier component of alpha(t) evaluated along the classical trajectory with mean action (Ju+Jv)/2. Numerical calculations for one- and two-dimensional systems show good agreement between quantum and classical results. The generalization to the case of N degrees of freedom is made. Thus, phase-space averaging within the quantized uncertainty volume provides a useful way to establish the classical-quantum correspondence for the linear and nonlinear response functions of a quasiperiodic system.

Journal Article↗

PubMed1976

On the lifetime-width relation for a decaying state and the uncertainty principle.

A new formulation of the uncertainty relation of position and momentum, and of energy and time, is presented. The connection between the lifetime of excited states and the energy width of these states, which does not follow from the usual uncertainty relation, is shown to be a consequence of the expression here derived.

Journal Article↗

PubMed1981

The effects of force and direction uncertainty of choice reaction time in an isometric force production task.

The two experiments reported examined the temporal organization of force and direction motor-programming processes in a step-input tracking type task. Both experiments observed a reduction in reaction time in the direction-uncertain conditions compared to the direction-certain ones. Thus it seems as though the direction decision does not have to precede the selection of the proper amount of forces. Experiment 2 observed an under-additive interaction between levels of direction uncertainty (certain or uncertain) and levels of force uncertainty (certain or uncertain). This interaction was interpreted as support for the programming of force and direction and thus, strongly supports the parallel model of programming recently proposed by Klapp (1977a,b).

Journal Article↗

PubMed2006

Optimization of the procedure for the determination of polycyclic aromatic hydrocarbons and their derivatives in fish tissue: Estimation of measurements uncertainty.

Three alternative procedures were employed for the isolation of polycyclic aromatic hydrocarbons (PAHs; 15 of 16 US EPA priority pollutants and benzo[e]pyrene), their methyl-derivatives and sulphur analogues from fish tissue: (1) Soxhlet extraction, (2) batch extraction enhanced by sonication, and (3) saponification of the sample followed by re-extraction of analytes into hexane. Soxhlet extraction using hexane-acetone (1:1, v/v) was the most efficient extraction technique, with analyte recoveries in the range 70-108%. Within optimization of the clean-up step, several types of gel permeation chromatography (GPC) systems were tested: two types of polystyrene divinylbenzene copolymer gels (PSDVB), both 'soft' gel type (Bio-Beads S-X3) and 'rigid' gels type (PL gel and Envirogel) in combination with various mobile phases were compared. Bio-Beads S-X3 and mobile phase chloroform were the most appropriate for purifying of crude extracts before the final determinative step. High-performance liquid chromatography with fluorimetric detection (HPLC/FLD) was used for identification and quantification of PAHs in purified fish extracts. The uncertainties of PAHs measurements were estimated by employing two alternative approaches. Both provided similar results: the expanded uncertainties obtained for individual PAHs by the 'top-down' approach were in the range 9-53%, their values resulting from application of the 'bottom-up' approach were in the range 16-52%.

Animals↗

PubMed1990

The effect of decision analysis on clinical uncertainty at tumor board.

Decision analysis is a formal approach to clinical decision making in the setting of uncertainty. Computer assisted clinical decision analysis was used at tumor board to help examine difficult oncological cases. Patients were identified early in the week and the decisions, possible outcomes, and uncertainties of each decision were modeled. These models were then presented at tumor board where the calculated expected utilities of each decision could be discussed. A description of decision analysis and three representative cases are presented here. These exercises were valuable for at least two reasons. First, modeling the problems confronting practicing oncologists was instructive as such. Second, the mathematical treatment of the probabilities and the utilities of the various outcomes for each decision stimulated a lively debate among the board members, forcing them to quantify probabilities and outcomes that they had previously ascertained qualitatively.

Bayes Theorem↗

PubMedDate not supplied

Assessment of uncertainty in mechanical testing of dental materials.

A generally valid and commonly accepted model for assessing the reliability of measurements in the field of medical and dental materials is hard to establish. The results obtained in different laboratories sometimes are difficult to compare. We therefore discuss different assessors of the quality of measurements from both conceptual and operational perspectives. Especially addressed are the customary terms accuracy, error and uncertainty, these terms that often are mixed rather confusingly in expressing the quality of experiments. The aim of this work is to present the advantages of choosing uncertainty rather than error as the appropriate assessor of the reliability of measurements. The transverse deflection testing of four denture-base acrylic resins served as an experimental basis for the analysis.

Acrylic Resins↗

PubMed1997

Evaluation of the uncertainty of molecular mass measurement by electrospray ionization mass spectrometry.

Electrospray ionization (ES) is a novel method used in mass spectrometry (MS) for producing gas-phase ions from substances in solutions. Common practices for molecular mass estimation from ES spectra summarize the spectrum as a single peak giving no estimate of uncertainty or treat each peak as an independent molecular mass measurement. ES-MS data analysis showed that each peak in an ES spectrum does not always provide an independent measure of molecular mass. Underestimation of measurement uncertainty is a possible result. An elementary time series method, the Yule-Walker equations, was applied to molecular mass estimation from ES data.

Animals↗

PubMed2002

Geographic origin of human mitochondrial DNA: accommodating phylogenetic uncertainty and model comparison.

Many biogeographic problems are tested on phylogenetic trees. Typically, the uncertainty in the phylogeny is not accommodated when investigating the biogeography of the organisms. Here we present a method that accommodates uncertainty in the phylogenetic trees. Moreover, we describe a simple method for examining the support for competing biogeographic scenarios. We illustrate the method using mitochondrial DNA sequences sampled from modern humans. The geographic origin of modern human mtDNA is inferred to be in Africa, although support for this hypothesis was ambiguous for data from an early paper.

Africa↗

PubMed1995

Evaluation of the use of uncertainty factors in deriving RfDs for some chlorinated compounds.

Risk assessment of exposure to chemicals having a toxic endpoint routinely uses the reference dose (RfD) approach based on uncertainty factors of 10. The purpose of this investigation was to evaluate whether the magnitude of the U.S. Environmental Protection Agency (EPA) 10x uncertainty factors has scientific merit when compared with data from recent human and animal experimental studies. A compilation and comparison of ratios between LOAEL/NOAEL (lowest observed adverse effect level/no observed adverse effect level) and subchronic/chronic values was made for six chlorinated compounds, namely, carbon tetrachloride, methylene chloride, pentachlorophenol, monochlorobenzene, chlorpyrifos, and 1,1-dichloroethane. Data sets demonstrated that 91.3% of the LOAEL/NOAEL ratios were < or = 6 while 87% of the ratios for the same parameter were < or = 5. Furthermore, subchronic/chronic ratios were < or = 3.5. From our investigation we concluded that automatic safety factors of 10x are not scientifically supportable and are overly conservative for the chlorinated compounds studied here.

Animals↗

PubMed1998

Visual search for a tilted target: tests of spatial uncertainty models.

We report that spatial cueing of a parafoveal target in the presence of distractors enhances orientational acuity for that target. When no distractors were present, orientation thresholds were in the range 1-4 degrees. For long exposure times, distractors increased threshold by the amount predicted from a winner-takes-all spatial uncertainty model. For short (100-msec) exposures followed by a random dot mask, the rise in threshold with distractors was considerably greater than that predicted from spatial uncertainty. For brief exposures the effect of distractors was greater when the target and distractors were spatially crowded rather than widely spaced. Adding a tilt to the distractors in the opposite direction to the target increased thresholds still further. Cueing the target with a spatial pointer decreased the effect of distractors, even when they were crowded. We suggest that when attention cannot be appropriately focused, discrimination is carried out by a relatively coarse texture analyser, which averages over several elements, and that focused attention permits the analysis of the target over a smaller area of space.

Attention↗