SEARCH · PubMed Health

Results for “Error minimization”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 613 records · Page 34Linked to original sources

PubMed2006

Psychophysiological training of operators in adaptive biofeedback cardiorhythm control.

A new individual computerized technique for psychophysiological training of operators before performing psychomotor activity on a computer model (psychomotor concentration and spatial orientation test) was developed. Qualitative criteria for the prediction of safe operator activity were formulated. Preliminary testing of operators' activity quality showed great dispersion of individual results: The amount of errors ranged from 0 to 56 and the rate of information processing varied from 1.01 up 3.56 bit/s. Subjects with initially identified respiratory sinus arrhythmia or synchronization caused by respiratory movements committed minimal recognition errors in initial stages at a high rate of information processing. The number of errors remained unchanged after the biofeedback cardio-training cycle, with the rate of information processing increasing noticeably. Subjects without inherent harmonics developed harmonics after sessions of cardiorhythm biofeedback control, and their operator activity quality improved significantly, making fewer mistakes and increasing the rate of information processing. Biofeedback control led not only to the restoration of respiratory sinus arrhythmia, a favorable diagnostic sign, as revealed by cardiorhythmograms, but also resulted in improvement of the quality of operator activity.

Adolescent↗

PubMed1976

Errors of parameters of distribution functions for spherical bodies stochastically estimated with parallel test lines of regular and narrow intervals.

The parameters of some distribution functions for the radius of spherical bodies randomly dispersed in a three-dimensional space can be estimated with a grating of parallel test lines of regular intervals superposed on a test plane of unit surface area. The interval of the test lines is set narrower than the mean diameter of the circles on the test plane. The errors of number Nlambdao of chords per test line of unit length, arithmetical mean lambda and secondary moment (lambda2) of the length of individual chords are: [C(Nlambdao)*]2=(4/9pi)(Q3/Q2(2))(1/M2lambdaNlambdao)+(4/pi)(lambda/Nlambdao), [C(lambda)*]2=(pi/4)[(32/3pi2) - 1](1/M2lambdaNlambdao)+[(4/pi)-(3pi/8)(Q2(2)/Q3)](lambda/Nlambdao) and [C(lambda2)*]2 = (1024/2025pi)(Q5Q3/Q4(2))(1/M2lambdaNlambdao)+4[(4/pi)-(3pi/8)(Q2(2)/Q3)](lambda/Nlambdao). The first and second terms of the right sides of these expressions represent intraregional and interregional errors, respectively; * denotes the error for the total region; M is the expectation of the number of test lines of unit length covering the test plane; and Qn a quotient (Dn)/Dn of sphere diameter D, n being a positive integer. Intraregional errors are inversely proportional to M2 with the grating, while they are inversely proportional only to M with random test lines. The use of regularly arranged test lines is consequently effective in minimizing intraregional errors.

Mathematics↗

PubMed1994

Clarification of chromosome nomenclature in the sheep (Ovis aries). Report of the committee for the standardization of the sheep karyotype.

In gene mapping, it is obviously essential that gene assignment errors are minimized. Recently, confusion has arisen in sheep gene mapping, as a result of contradictions in chromosome nomenclature. The purpose of this brief communication, prepared by the International Sheep Karyotype Standardization Committee, is to minimize any further confusion that may arise, while new sheep standard Q, G and R karyotypes and ideograms are being prepared. This paper reviews the history of previous sheep karyotype standards, explains the errors that have been detected and presents a correlation table so that, whichever nomenclature is used, the exact chromosome can be identified.

Animals↗

PubMed1964

THE PREOPERATIVE ASSESSMENT OF MULTIPLE VALVE DISEASE.

Representative case histories are used to discuss the difficulties in preoperative assessment of patients with multiple valve disease and the dangers of correcting one lesion when two or more valves are seriously damaged. Errors fall into three broad categories: existing second valve disease (1) may not be suspected, (2) may be considered insignificant or (3) may be considered a consequence of the first.Recommendations are offered to minimize these errors. The four valves should be studied physiologically, no matter how "normal" the other three may appear to be clinically, whenever open-heart surgery is contemplated. In bivalvular disease angiographic methods are preferable to pressure studies, for data so obtained are not dependent on cardiac output. Mitral and tricuspid regurgitation can never be attributed with certainty to a more distal lesion but require direct examination at time of operation for assessment.

Angiography↗

PubMedDate not supplied

Baboon basal ganglia stereotaxy using internal MRI landmarks: validation and application to PET imaging.

PURPOSE: We report the residual anatomic error after a nine parameter visually guided registration of MR images with a baboon brain atlas to validate a stereotactic method for use in PET studies. METHOD: MPRAGE images of brain in six baboons and one nemestrina monkey were placed in atlas space using internal landmarks and proportional measurements. An expert noted the location of 23 subcortical test points in the transformed images and in the atlas. RESULTS: The average absolute error at the test points was 1.62 mm. At the extremes of the brain surface, there was more variability. PET images could be combined across animals in a common atlas space. CONCLUSION: There is minimal subcortical error attributable to anatomic variability after this method of transforming MR images of baboon to stereotactic space. This method provides a useful tool for intrasubject PET baboon studies as well as "bootstrapping" for more refined methods.

Animals↗

PubMed2001

Statistical mechanics of learning with soft margin classifiers.

We study the typical learning properties of the recently introduced soft margin classifiers (SMCs), learning realizable and unrealizable tasks, with the tools of statistical mechanics. We derive analytically the behavior of the learning curves in the regime of very large training sets. We obtain exponential and power laws for the decay of the generalization error towards the asymptotic value, depending on the task and on general characteristics of the distribution of stabilities of the patterns to be learned. The optimal learning curves of the SMCs, which give the minimal generalization error, are obtained by tuning the coefficient controlling the trade-off between the error and the regularization terms in the cost function. If the task is realizable by the SMC, the optimal performance is better than that of a hard margin support vector machine and is very close to that of a Bayesian classifier.

Algorithms↗

PubMed1996

Error bounds on ultrasonic scatterer size estimates.

Precision errors that occur in estimating the average scatterer size from pulse-echo ultrasound waveforms are examined in detail. The method-independent lower bound on estimation error is found from the Cramér-Rao inequality for comparison with the predicted error for the measurement technique currently used to estimate scatterer sizes in soft biological tissues. The probability density function for the estimate is also derived. From these statistical analyses, strategies for designing experiments that minimize the error are discussed. It is shown that compared with biological variability, measurement errors in scatterer size estimates are relatively large. Consequently, there is reason to continue searching for more efficient estimators. Although the analysis and results are derived for Gaussian correlation models that have been used to study the function and structure of kidneys, generalization to include correlation models for other tissues is straightforward.

Models, Biological↗

PubMed2006

The effect of enslaving on perception of finger forces.

The primary purpose was to examine the effect of enslaving on finger force perception during isometric finger force production using an ipsilateral force-matching paradigm. Fourteen subjects were instructed to produce varying levels of reference forces [10, 20, 30, and 40% maximal voluntary contraction (MVC)] force using one finger (index, I or little, L) and to reproduce these forces using the same finger (homo-finger tasks, I/I and L/L) or a different finger (hetero-finger tasks, I/L and L/I). Forces of all fingers were recorded. During homo-finger tasks, no differences were found in force magnitude or relative level of force (expressed as a proportion of MVC). The index finger matching force magnitudes were greater than the little finger reference force magnitudes, with significantly lower levels of relative force during L/I tasks; while the little finger matching forces underestimated the index finger reference forces with significantly higher levels of relative force during I/L tasks. The difference in the matching and reference forces by the instructed finger(s), i.e., matching error, was larger in hetero-finger tasks than in homo-finger tasks, particularly at high reference force levels (30, 40% MVC). When forces of all fingers were considered, enslaving (uninstructed finger forces) significantly minimized matching errors of the total force during both I/L and L/I hetero-finger tasks, especially at high reference force levels. Our results show that there is a tendency to match the absolute magnitude of the total force during ipsilateral finger force-matching tasks. This tendency is likely related to enslaving effects. Our results provide evidence that all (instructed and uninstructed) finger forces are sensed, thus resulting in perception of the absolute magnitude of total finger force.

Adult↗

PubMed2002

Fuzzy control of multivariable process by modified error decoupling.

In this paper, a control concept for the squared (equal number of inputs and outputs) multivariable process systems is given. The proposed control system consists of two parts, single loop fuzzy controllers in each loop and a centralized decoupling unit. The fuzzy control system uses feedback control to minimize the error in the loop and the decoupler uses an adaptive technique to mitigate loop interactions. The decoupler predicts the interacting loop changes and modifies the input (error) of the loop controller. The controller was tested on the simulation model of "single component vaporizer" process. The results indicate that the decoupling controller shows better performance for set point and load changes.

Algorithms↗

PubMed2004

Correction of sequence-based artifacts in serial analysis of gene expression.

MOTIVATION: Serial Analysis of Gene Expression (SAGE) is a powerful technology for measuring global gene expression, through rapid generation of large numbers of transcript tags. Beyond their intrinsic value in differential gene expression analysis, SAGE tag collections afford abundant information on the size and shape of the sample transcriptome and can accelerate novel gene discovery. These latter SAGE applications are facilitated by the enhanced method of Long SAGE. A characteristic of sequencing-based methods, such as SAGE and Long SAGE is the unavoidable occurrence of artifact sequences resulting from sequencing errors. By virtue of their low-random incidence, such tag errors have minimal impact on differential expression analysis. However, to fully exploit the value of large SAGE tag datasets, it is desirable to account for and correct tag artifacts. RESULTS: We present estimates for occurrences of tag errors, and an efficient error correction algorithm. Error rate estimates are based on a stochastic model that includes the Polymerase chain reaction and sequencing error contributions. The correction algorithm, SAGEScreen, is a multi-step procedure that addresses ditag processing, estimation of empirical error rates from highly abundant tags, grouping of similar-sequence tags and statistical testing of observed counts. We apply SAGEScreen to Long SAGE libraries and compare error rates for several processing scenarios. Results with simulated tag collections indicate that SAGEScreen corrects 78% of recoverable tag errors and reduces the occurrences of singleton tags. AVAILABILITY: The SAGEScreen software is available for academic users from the first author.

Algorithms↗

PubMedDate not supplied

Analyzing the uncorrected error of dilution water demand for the dilution biochemical oxygen demand method.

Dilution water demand (DWD) can cause a positive error when the dilution biochemical oxygen demand (BOD) method is used. Dilution water demand may be attributed to oxidation of organic impurities in the dilution water and nitrification of ammonia added as a nutrient. To minimize the error associated with these sources, the standard BOD method requires that DWD be less than 0.2 mg/L in 5 days and does not allow correction for DWD when calculating test results. This study derives a set of theoretical equations to analyze the uncorrected errors with and without seeding. The authors concluded that DWD can be completely corrected if seeded dilution water is used for the sample dilution. When seeding individual bottles, the uncorrected error approaches 8.3 to approximately 8.8% at a 5-day depletion of 2 mg/L for a typical secondary effluent. Tests without seeding show an almost 1% higher uncorrected error than seeded tests. The analysis also suggests that these errors can be effectively reduced to less than 3% when the 5-day depletion approaches 6 mg/L. even for 5-day biochemical oxygen demand concentrations exceeding I x 10(4) mg/L. Further analysis indicates that, if not inhibited, the ammonium added to dilution water as a nutrient may contribute additional error due to nitrification.

Ammonia↗

PubMed1991

Fuzzy K-nearest neighbor classifiers for ventricular arrhythmia detection.

We report a study of the efficiency of 4 classifiers (the K-nearest-neighbor and single-nearest-prototype algorithms, each as parametrized by both Fuzzy C-Means and Fuzzy Covariance clustering) in the detection of ventricular arrhythmias in ECG traces characterized by 4 features derived from 7 spectral parameters. Principal components analysis was used in conjunction with a cardiologist's deterministic classification of 90 ECG traces to fix the number of trace classes to 5 (ventricular fibrillation/flutter, sinus rhythm, ventricular rhythms with aberrant complexes and 2 classes of artefact). Forty of the 90 traces were then defined as a test set; 5 different learning sets (numbering 25, 30, 35, 40 and 45 traces) were randomly selected from the remaining 50 traces; each learning set was used to parametrize both the classification algorithms using both fuzzy clustering algorithms and the parametrized classification algorithms were then applied to the test set. Optimal K for K-nearest-neighbor algorithms and optimal cluster volumes for Fuzzy Covariance algorithms were sought by trial and error to minimize classification differences with respect to the cardiologist's classification. Fuzzy Covariance clustering afforded significantly better perception of cluster structure than the Fuzzy C-Means algorithm, and the classifiers performed correspondingly with an overall empirical error ratio of just 0.10 for the K-nearest-neighbor algorithm parametrized by Fuzzy Covariance.

Algorithms↗

PubMed2004

Possible errors in pin insertion positions using the C-arm.

In order to measure errors in pin positions, a tibia with referenced pin insertions was radiographed in various locations using a mini C-arm. Changes in pin position locations up to seven millimeters and twelve degrees were found. To minimize these errors, limbs should be centered and parallel to the plane of the imaging screen of the C-arm. If possible, pin insertions should be made in this plane. Magnification due to the distance from the screen should be determined for precise pin positioning.

Bone Nails↗

PubMed2000

On the optimality of the gridding reconstruction algorithm.

Gridding reconstruction is a method to reconstruct data onto a Cartesian grid from a set of nonuniformly sampled measurements. This method is appreciated for being robust and computationally fast. However, it lacks solid analysis and design tools to quantify or minimize the reconstruction error. Least squares reconstruction (LSR), on the other hand, is another method which is optimal in the sense that it minimizes the reconstruction error. This method is computationally intensive and, in many cases, sensitive to measurement noise. Hence, it is rarely used in practice. Despite their seemingly different approaches, the gridding and LSR methods are shown to be closely related. The similarity between these two methods is accentuated when they are properly expressed in a common matrix form. It is shown that the gridding algorithm can be considered an approximation to the least squares method. The optimal gridding parameters are defined as the ones which yield the minimum approximation error. These parameters are calculated by minimizing the norm of an approximation error matrix. This problem is studied and solved in the general form of approximation using linearly structured matrices. This method not only supports more general forms of the gridding algorithm, it can also be used to accelerate the reconstruction techniques from incomplete data. The application of this method to a case of two-dimensional (2-D) spiral magnetic resonance imaging shows a reduction of more than 4 dB in the average reconstruction error.

Algorithms↗

PubMed2003

The importance of cognitive errors in diagnosis and strategies to minimize them.

In the area of patient safety, recent attention has focused on diagnostic error. The reduction of diagnostic error is an important goal because of its associated morbidity and potential preventability. A critical subset of diagnostic errors arises through cognitive errors, especially those associated with failures in perception, failed heuristics, and biases; collectively, these have been referred to as cognitive dispositions to respond (CDRs). Historically, models of decision-making have given insufficient attention to the contribution of such biases, and there has been a prevailing pessimism against improving cognitive performance through debiasing techniques. Recent work has catalogued the major cognitive biases in medicine; the author lists these and describes a number of strategies for reducing them ("cognitive debiasing"). Principle among them is metacognition, a reflective approach to problem solving that involves stepping back from the immediate problem to examine and reflect on the thinking process. Further research effort should be directed at a full and complete description and analysis of CDRs in the context of medicine and the development of techniques for avoiding their associated adverse outcomes. Considerable potential exists for reducing cognitive diagnostic errors with this approach. The author provides an extensive list of CDRs and a list of strategies to reduce diagnostic errors.

Cognition↗

PubMed1996

On the recording of sample times and parameter estimation from repeated measures pharmacokinetic data.

A pharmacokinetic screen has been advocated for the characterization of the population pharmacokinetics of drugs during Phase 3 clinical trials. A common perception encountered in the collection of such data is that the accuracy of sampling times relative to dose is inadequate. A prospective simulation study was carried out to evaluate the effect of error in the recording of sampling times on the accuracy and precision of population parameter estimates from repeated measures pharmacokinetic data. A two-compartment model with intravenous bolus input(s) (single and multiple doses) was assumed. Random and systematic error in sampling times ranging from 5-50% using profile (block) randomized design were introduced. Sampling times were simulated in EXCEL while concentration data simulation and analysis were done in NONMEM. The effect of error in sampling times was studied at levels of variability ranging from 15-45% for a drug assumed to be dosed at its elimination half-life. One hundred replicate data sets of 100 subjects each were simulated for each case. Although estimates of clearance (CL) and variability in clearance were robust for most of the sampling time errors, there was an increase in bias and imprecision in overall parameter estimation as intersubject variability was increased. If there is interest in parameters other than CL, then the design of prospective population studies should include procedures for minimizing the error in the recording of sample times relative to dosing history.

Computer Simulation↗

PubMed2005

Implementation of LOCAL algorithm with near-infrared spectroscopy for compliance assurance in compound feedingstuffs.

Seven thousand four hundred and twenty-three compound feed samples were used to develop near-infrared (NIR) calibrations for predicting the percentage of each ingredient used in the manufacture of a given compound feedingstuff. Spectra were collected at 2 nm increments using a FOSS NIRSystems 5000 monochromator. The reference data used for each ingredient percentage were those declared in the formula for each feedingstuff. Two chemometric tools for developing NIRS prediction models were compared: the so-called GLOBAL MPLS (modified partial least squares), traditionally used in developing NIRS applications, and the more recently developed calibration strategy known as LOCAL. The LOCAL procedure is designed to select, from a large database, samples with spectra resembling the sample being analyzed. Selected samples are used as calibration sets to develop specific MPLS equations for predicting each unknown sample. For all predicted ingredients, LOCAL calibrations resulted in a significant improvement in both standard error of prediction (SEP) and bias values compared with GLOBAL calibrations. Determination coefficient values (r(2)) also improved using the LOCAL strategy, exceeding 0.90 for most ingredients. Use of the LOCAL algorithm for calibration thus proved valuable in minimizing the errors in NIRS calibration equations for predicting a parameter as complex as the percentage of each ingredient in compound feedingstuffs.

Algorithms↗

PubMed1991

Methodological error and spatial variability of organ blood flow measurements using radiolabeled microspheres.

The quantitative analysis of the spatial variability of organ blood flow by means of radiolabeled microspheres (MS) requires that the methodological variability ("error") of the technique (RDmeth.) is known in each individual organ. Therefore, RDmeth. was quantified (eight to nine nuclides) in 6941 tissue samples from 13 organs of three anesthetized dogs, and the relative importance of errors originating from both the stochastic nature of MS distribution (RDtheo.) and the process of quantitation of MS radioactivity (RDcounting) was assessed under varying conditions (high/low specific MS activity (SAMS); inaccurate separation of gamma spectra; large sample size). At "minimized" methodological error (experiment 2), RDmeth. of samples trapping approximately 375 MS/nuclide was 5.8% and only slightly exceeded RDtheo. (5%). RDmeth. varied in the range 2.7-7.8% in individual organs and contributed little (3.5%) to the organs' observed spatial variability of flow. In contrast, RDmeth.--due to increased RDcounting--considerably exceeded RDtheo. when SAMS was low (experiment 3), overlap of two nuclides' main photopeaks was critical (experiment 1), or counting geometry was inappropriate (pulmonary tissue samples). At the same time, the contribution of RDmeth. to spatial flow variability rose to 7.9% (experiment 3), 26.9% (experiment 1), and 15-23% (lungs). Completely artifactual measurements, as indicated by an extremely high RDmeth. of sample flow, were rarely observed (less than 0.1%). In general, our data suggest that blood flow can be measured reproducibly and with low methodological error using up to 8 nuclides, RDmeth. does not essentially contribute to the observed spatial variability of organ blood flow, and, hence, organ flow variability may be accurately quantified using the MS technique. However, if sources of error as indicated above are present, the practice of using RDtheo. as a measure of RDmeth. (thereby neglecting RDcounting) may notably underestimate true MS error and result in an overestimation of spatial heterogeneity of organ blood flow. RDmeth., therefore, should be quantified separately in each region of interest prior to the onset of a new study.

Animals↗