[Failures and error sources in indirect inlay technic. B. Error sources in the laboratory].
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Inlays↗
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Results for “Error Sources”
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Error budgets: a system to characterize error source in health care experimentation.
OBJECTIVE: In the design of an experiment, it is important that all significant sources of error be identified and characterized accurately before the experiment is executed. For many experiments, the experiment designer is less inclined to ignore significant error factors when he adopts the use of an error budget in his experiment design process. A plan for generating an accurate error budget is presented along with a discussion concerning the disposition of significant error sources. METHODS: Specific methods discussed to generate the error budget are the fishbone diagram, factor weighing and Pareto analysis. Specific dispositions suggested are to eliminate, attenuate, characterize or to simply acknowledge the error with no remedy. These procedures, adhered to by most successful experiment design teams in industry, have evolved over recent decades and seem to be of use as they are applied to health care research. RESULTS: Use of the outlined method forces the experimenter to become familiarized with the most significant variables of the experiment he or she is designing through the deliberate examination of experimental noise contributors and through the comparison of the experimental noise to the magnitudes of the measurements in the experiment. CONCLUSION: The design of health care research experiments may be streamlined by incorporating the methods outlined in the generation of an error budget and by properly using the error budget to dispose of each source of error properly.
Chiropractic↗
An investigation of error sources and their impact in estimating the time to the most recent ancestor of spatially and temporally distributed HIV sequences.
This is an investigation of significant error sources and their impact in estimating the time to the most recent common ancestor (MRCA) of spatially and temporally distributed human immunodeficiency virus (HIV) sequences. We simulate an HIV epidemic under a range of assumptions with known time to the MRCA (tMRCA). We then apply a range of baseline (known) evolutionary models to generate sequence data. We next estimate or assume one of several misspecified models and use the chosen model to estimate the time to the MRCA. Random effects and the extent of model misspecification determine the magnitude of error sources that could include: neglected heterogeneity in substitution rates across lineages and DNA sites; uncertainty in HIV isolation times; uncertain magnitude and type of population subdivision; uncertain impacts of host/viral transmission dynamics, and unavoidable model estimation errors. Our results suggest that confidence intervals will rarely have the nominal coverage probability for tMRCA. Neglected effects lead to errors that are unaccounted for in most analyses, resulting in optimistically narrow confidence intervals (CI). Using real HIV sequences having approximately known isolation times and locations, we present possible confidence intervals for several sets of assumptions. In general, we cannot be certain how much to broaden a stated confidence interval for tMRCA. However, we describe the impact of candidate error sources on CI width. We also determine which error sources have the most impact on CI width and demonstrate that the standard bootstrap method will underestimate the CI width.
Animals↗
Point-of-care testing error: sources and amplifiers, taxonomy, prevention strategies, and detection monitors.
CONTEXT: In a survey performed 4 years ago, testing venues doing only point-of-care testing (POCT) made up 78% of sites for patient testing licensed under federal regulations. OBJECTIVES: To identify sources of POCT error, to present a classification of such errors, to suggest strategies to prevent errors, and to describe monitors that assess and reduce the frequency of errors. DESIGN: To identify sources of POCT error, large studies of error among US Federal Certificate of Waiver laboratories (CoWs) and practitioner-performed microscopy certificate holders were reviewed. To facilitate investigation and management of POCT error, a taxonomy of such errors (modified from a classification previously published by Gerald Kost) was used to identify 4 steps with error potential in each of the 3 phases (ie, preanalytic, analytic, and postanalytic) of the POCT process. To prevent observed POCT errors, 4 strategies are suggested: direct observation of instrument/method functionality, structured observation of method performance, proficiency testing/use of relevant test scenarios, and autonomation. To assess frequency of errors, a quartet of indices are introduced as detection monitors: order documentation, patient identification, specimen adequacy, and result integrity. RESULTS: Three sources of POCT error were identified: operator incompetence, nonadherence to test procedures, and use of uncontrolled reagents and equipment. Three other characteristics of many point-of-care tests amplify their risk of error: incoherent regulation, rapid availability of results, and the results' immediate therapeutic implications. Two members of the quartet of detection monitors, order documentation and specimen adequacy, are relatively difficult to measure and are controversial, but the other 2, patient identification and result integrity, are easier to assess and are relatively widely accepted. CONCLUSIONS: Point-of-care testing errors are relatively common, their frequency is amplified by incoherent regulation, and their likelihood of affecting patient care is amplified by the rapid availability of POCT results and the results' immediate therapeutic implications. The modified Kost taxonomy offers a reasonable approach to the identification of POCT errors. Direct observation of test functionality, structured observation of test performance, and testing the competence of POCT operators, as well as autonomation of devices, are strategies to prevent such errors. In this context, we suggest monitoring POCT order documentation, patient identification, specimen integrity, and result reporting to detect errors in this sort of testing.
Humans↗
Pulsed Doppler accuracy assessment due to frequency-dependent attenuation and Rayleigh scattering error sources.
All engineering measurements are subject to inaccurate and imprecise estimates, including the estimate of blood flow velocity. An assessment of specific error sources can minimize such uncertainties. Frequency-dependent attenuation and Rayleigh scattering are significant error sources for pulsed Doppler ultrasound because the transmitted ultrasonic signal has a finite width spectrum. The former causes a frequency downshift and the latter a frequency upshift, both of which are independent of the actual Doppler frequency shift. This communication evaluates these error sources through computer stimulation and compares the computed error to experimental data.
Blood Flow Velocity↗
[Quantitation of regional cerebral blood flow using 123I-IMP from a single SPECT scan and a single blood sampling--analysis on statistical error source and optimal scan time].
Recently, a method has been proposed to measure quantitative regional cerebral blood flow (rCBF) in man using N-isopropyl-p-[123I]-iodoamphetamine (IMP) and single photon emission tomography (SPECT). In this method (IMP-ARG method), a functional map of rCBF was calculated from a single SPECT scan data set, in which effects of the clearance of IMP from the brain was taken into account by employing the 2 compartment model. To avoid the procedures of frequent and/or continuous sampling of the arterial blood that was required in determination of the input function, use of a standard input function and calibrating it by one blood sampling were validated. The present study was intended to investigate the sensitivity to various sources of errors in the IMP-ARG method such as (1) effects of individual difference of the arterial input function, (2) effects of ambiguity of the regional distribution volume (Vd) of IMP, and (3) effects of inaccuracy of the SPECT measurement. It was shown in the present simulation study that errors in the calculated rCBF values were dependent on the SPECT mid-scan time (MST), and that the minimum error corresponded to the MST of approximately 30 min after the IMP infusion. With this optimal MST, errors in rCBF due to the individual difference of the input function was approximately 10%, and the errors due to the ambiguity of the Vd were approximately 8%. The total accuracy of the calculated rCBF in the IMP-ARG method was, therefore, estimated as approximately 13%. Although a relatively large error was expected at a high rCBF area, this study strongly suggested the IMP-ARG method being useful and accurate for providing the quantitative rCBF map for a clinical use.
Amphetamines↗
[The analysis of error sources for SAM and its improvement algorithms].
Based on the analysis of the error sources for spectral anglemapping (SAM), several key elements are pointed out, i.e. the change of wave band location, the change of the attribution ratio, the random change of attribution, and the whole translation of wave band. After the above-mentioned four error sources are analyzed, the authors present several improvement algorithms, viz. calculating the spectral angle with grouping, normalization and intersection. The grouping method can resolve the pseudo-similar problem, because it considers both spectral global features and local features. Calculating spectral angle with normalization restrains those random errors in original data by normalizing the spectral vectors. The intersection method can eliminate the error elicited by the whole wave translation. Therefore, it can be employed to correctly identify spectral class. Experiments show that those improvement algorithms are effective and can be used to process spectral data with errors.
Algorithms↗
Experimental analysis of error sources in fibre type counts of biopsies in horses.
The contribution to total variance of different error sources in fibre type counts of equine gluteus medius muscle biopsies was determined to quantify and possibly improve the resolution of the method. Fibre types were defined on the basis of myosin heavy chain immunostaining. Errors were determined at levels: (1) positioning the insertion channel, (2) positioning the needle tip (3) biopsy heterogeneity (4) observer interpretation. Errors at levels 1 and 2 were considerable. Confidence intervals for individual observations were +/- 10-15%. In longitudinal studies a group size of 4 animals is necessary to resolve fibre composition changes of 10%. Comparison with multiple counts on post mortem specimens showed that local muscle fibre heterogeneity is responsible to a considerable extent for the error variance. Variance is effectively reduced by processing 3-4 shavings from the same insertion channel.
Animals↗
Error sources and algorithms for white-light fringe estimation at low light levels.
We address the problem of highly accurate phase estimation at low light levels, as required by the Space Interferometry Mission (SIM). The most stringent SIM requirement in this regard is that the average phase error over a 30-s integration time correspond to a path-length error of approximately 30 pm. Most conventional phase-estimation algorithms exhibit significant enough bias at the signal levels at which the SIM will be operating so that some correction is necessary. Several algorithms are analyzed, and methods of compensating for their bias are developed. Another source of error in phase estimation occurs because the phase is not constant over the integration period. Errors that are due to spacecraft motion, the motion of compensating optical elements, and modulation errors are analyzed and simulated. A Kalman smoothing approach for compensating for these errors is introduced.
Journal Article↗
Error sources affecting thermocouple thermometry in RF electromagnetic fields.
Thermocouple thermometry errors in radiofrequency (typically 13, 56 MHZ) electromagnetic fields such as are encountered in hyperthermia are described. RF currents capacitatively or inductively coupled into the thermocouple-detector circuit produce errors which are a combination of interference, i.e., 'pick-up' error, and genuine rf induced temperature changes at the junction of the thermocouple. The former can be eliminated by adequate filtering and shielding; the latter is due to (a) junction current heating in which the generally unequal resistances of the thermocouple wires cause a net current flow from the higher to the lower resistance wire across the junction, (b) heating in the surrounding resistive material (tissue in hyperthermia), and (c) eddy current heating of the thermocouple wires in the oscillating magnetic field. Low frequency theories are used to estimate these errors under given operating conditions and relevant experiments demonstrating these effects and precautions necessary to minimize the errors are described. It is shown that at 13.56 MHz and voltage levels below 100 V rms these errors do not exceed 0.1 degrees C if the precautions are observed and thermocouples with adequate insulation (e.g., Bailey IT-18) are used. Results of this study are being currently used in our clinical work with good success.
Diathermy↗
Structured noise in computed tomography: effects of periodic error sources.
The artifact in computed tomography (CT) images due to cyclic projection errors, such as errors due to periodic fluctuations in x-ray intensity, is derived and verified by computer simulation. Depending upon the relative phase of the error between projections, the artifact is shown to be described by a Bessel function (or functions) of the radial argument which is sinusoidally modulated as a function of angle. Because of the nature of Bessel functions, the artifact is essentially zero up to some minimum radius. When the effects of sampling are neglected, a single fundamental artifact is shown to occur. In fourth-generation scanners, the fundamental artifact (neglecting sampling) will occur at a detector fan angle of about about 39 degrees (depending on the ratio of the axis-to-detector, source-to-axis distances). The radius of appearance of this fundamental artifact is independent of the frequency of the periodic error signal and will only be visible in fourth-generation CT scanners with detector fan angles greater than about 39 degrees. The effects of sampling are derived and illustrated by simulation for first-, third-, and fourth-generation CT-scanner geometries. It is shown that the effect of sampling is to cause an infinite number of such artifacts to be superimposed in the final image. The radius of appearance of all but the fundamental artifact are shown to be dependent on the frequency of the periodic signal. It is shown that by judicious choice of the sampling parameters relative to the frequency of the periodic error, the artifact can be effectively eliminated.
Technology, Radiologic↗
Simulating refractive errors: source and observer methods.
There are two principal methods of simulating refractive errors. Either the retinal image can be defocused by an optical system, usually a positive lens, placed in front of an observer's eye (observer method), or the source of the retinal image can be defocused as it is projected onto a screen or photograph (source method). There are significant differences between the two methods, differences that make it difficult to compare results. However, the source method, which is the more artificial, seems to be superior for a number of reasons. The results of these two methods can be compared using a common or interchangeable parameter for specifying the level of defocus. A convenient parameter is the size of the defocused image of a point, measured either in image space (linear or angular diameter on the retina) or in object space (angular diameter of the blur disc projected back into object space), with the angular diameter measured from the respective nodal point of the eye. Methods of measuring the angular blur-disc diameter for both methods are discussed and the validity of the formula omega = D delta L, is investigated, where omega is the angular diameter of the blur disc, D is the observer's pupil diameter, and delta L is the dioptric defocus.
Humans↗
[More reliable blood pressure measurement by elimination of error sources].
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Blood Pressure Determination↗
[Error sources in recording three-dimensional mandibular movements. An in vitro study using the V-type stereognathograph].
The instrument-induced measurement errors in V-type stereognatography have been analyzed. An optical bench was used as a measurement apparatus. In measuring not too small movement distances, the linearity errors remained within acceptable limits. The variations in linearity due to calibration errors were almost negligible. In practical applications, the stereognatography proved to be insensitive to external factors such as type of illumination, room temperature and voltage fluctuations. Factors affecting the effectiveness of the projection error correction system, such as tilting of the filter, different sites of measurement of the six optoelectronic canals, and mandibular protrusion during mediotrusive movements, might be reduced by slight modifications of the measurement system.
Cephalometry↗
Assessment of diffusion coefficients of general solvents by PFG-NMR: investigation of the sources error.
Accurate measurements of the diffusion coefficients, including an estimate of uncertainty, of various solvent molecules using the PFG-NMR method were performed in this study. Accurate diffusion coefficients were obtained using the Shigemi NMR tube. The relative combined standard uncertainties of the diffusion coefficients were found to be within approximately 0.4%. The three uncertainty sources (signal decay of the standard and the solvent, and diffusion coefficient of standard) equally affect the combined standard uncertainties. Unreliable data were obtained using a normal NMR tube, indicating that convection and background gradient effects significantly affected the accurate measurement of the diffusion coefficients.
Journal Article↗
Reproducibility and error sources of micro-MRI-based trabecular bone structural parameters of the distal radius and tibia.
The mechanical competence of trabecular bone is significantly determined, next to material density, by its three-dimensional (3D) structure. Recent advances in micromagnetic resonance imaging (micro-MRI) acquisition and processing techniques allow the 3D trabecular structure to be analyzed in vivo at peripheral sites such as the distal radius and tibia. The practicality of micro-MRI-based noninvasive virtual bone biopsy (VBB) for longitudinal studies of patients hinges on the reproducibility of the derived structural parameters, which largely determine the size of the effect that can be detected at a given power and significance level. In this paper, the reproducibility of micro-MRI-derived trabecular bone structure measures was examined by performing repeat studies in six healthy subjects in whom the distal aspects of the radius and tibia were scanned with a 3D spin-echo sequence at 137 x 137 x 410 microm3 voxel size. Bone volume fraction (BV/TV) and digital topological analysis (DTA) structural parameters including the topological bone surface-to-curve ratio (SCR) and topological erosion index (TEI) were evaluated after subjecting the raw images to a cascade of processing steps. The average coefficient of variation was 4-7% and was comparable for the two anatomic sites and for all parameters measured. The reliability expressed in terms of the intraclass correlation coefficient ranged from 0.95 to 0.97 in the radius and 0.68 to 0.92 in the tibia. Error analysis based on simulations suggests involuntary patient motion, primarily rotation, to be the chief source of imprecision, followed by failure to accurately match the analysis volumes in repeat studies.
Adult↗
[Prognostication of foetal weight by means of ultrasonic foetometry. Study into accuracy of various formulae and analysis of error sources (author's transl)].
The author conducted a large-scale study into all accessible formulae for foetal weight assessment on the basis of ultrasonic measurement. Included were the author's own recently devised formulae. They were all studied for their accuracy, with reference being made to 100 unselected data groupings.--Another analysis was made for the purpose of finding out the extent to which the number of data used by different examiners could change differences between estimated results derived from formulae. Reference in great detail is made also to the effects of measurement errors and selection of data upon formula results.--Proper choice of measurement level was found to be important. Abdominal parameters proved to be superior to thoracic parameters. Estimated results, generally, improved along with the number of foetal measuring points, provided they were really relevant and weightful.--Discussed is the relative value which should be ascribed to all factors with impact on the accuracy of weight prognosis. Proper choice of an adequate mathematical model or adjustment of such choice to foetal data is considered to be essential, because it has to be made by optimum consideration of all factors.--All the above formulae were verified, but accuracies claimed earlier by original authors were reproducible only in some rare cases. The demand, therefore, is made that whenever new formulae are introduced the best of all available techniques of assessment should be used to compare their results, with reference to be made to the same, unselected patients. This is considered to be the best way for an objective assessment of their advantages.--An account is given of those practicable formulae which can be recommended, as a result of the comparison, and for which easy-to-use nomograms are available.
Anthropometry↗
Polyadenylated RNAs as error sources in ribosomal RNA turnover analyses.
An approach to ribosomal RNA turnover studies in which cytoplasmic RNA was extracted and subsequently fractionated to isolate ribosomal RNA is reported. The presumption that the pool of 28S and 18S RNAs represented ribosomal RNA, exclusively, proved false and led to erroneous results of ribosomal RNA turnover. Polyadenylated RNAs exhibited a heterogeneous size distribution and, although constituting only 3% (w/w) of the cytoplasmic RNA extract, accounted for fully 10% of radioactivity of the presumptive ribosomal RNA pool. Profiles from the radioactivity data suggested that the discrepant results were due to these polyadenylated RNAs. An additional analytical procedure, an oligo (dT) cellulose column chromatography of the RNA extract prior to the sucrose density gradient fractionation step, performed as described in this paper, proved an effective remedy for this error.
Animals↗