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At least 1,333 records · Page 74Linked to original sources
PubMed1998

Source monitoring: ERP evidence for greater reactivity to nontarget information in older adults.

Event-Related Potentials (ERPs) were collected concurrently with stimulus presentation during a source monitoring task. Younger adults were less likely than older adults to make source monitoring errors and their ERP records showed far greater discrimination between target stimuli and familiar but nontarget foils. Older adults not only made more source errors but produced high amplitude late positivities to the nontarget foils even when these foils were correctly rejected. Under divided attention conditions, younger adults performance was similar to that of the older adults both behaviorally and electrophysiologically. These data illustrate the role that attentional resources play in the ability to inhibit response tendencies and suggest that age differences in source monitoring may be more related to attentional control than inefficiencies in the encoding of contextual information. As well, they suggest that the ERP late positivity may represent a more general response to item salience rather than serve as an index of recollection as is the current view.

Aged↗
PubMed2004

Sources of variability and systematic error in mouse timing behavior.

In the peak procedure, starts and stops in responding bracket the target time at which food is expected. The variability in start and stop times is proportional to the target time (scalar variability), as is the systematic error in the mean center (scalar error). The authors investigated the source of the error and the variability, using head poking in the mouse, with target intervals of 5 s, 15 s, and 45 s, in the standard procedure, and in a variant with 3 different target intervals at 3 different locations in a single trial. The authors conclude that the systematic error is due to the asymmetric location of start and stop decision criteria, and the scalar variability derives primarily from sources other than memory.

Animals↗
PubMed1999

Cardiac output and central blood volume during hemodialysis: methodology.

Cardiovascular disease is the leading cause of mortality in patients whose lives depend on hemodialysis. We developed a method for measuring cardiac output (CO) and central blood volume (CBV) in hemodialyzed patients that may help to elucidate the mechanisms and consequences of cardiac disease in this population. This report describes the technique, focusing on the main sources of error and how they can be prevented. Three principal sources of error were identified: (1) access recirculation (existing or induced during injection); (2) the second pass of the indicator through the cardiopulmonary system, exacerbated by prolonging the duration of intravenous injection; and (3) the transit time of the indicator through the dialysis blood lines. After the algorithms were adjusted to prevent the above errors, the reproducibility of CO and CBV, expressed as the absolute percent deviation from the average of duplicates (3,488 values duplicated within 5 minutes), was 4.3 +/- 3.8% for CO and 4.1 +/- 3.8% for CBV. To determine the clinical value of routine CO and CBV measurements, morbid events (nausea, vomiting, and/or muscle cramps) were prospectively recorded in 73 randomly selected hemodialysis patients. CO and CBV were measured near the beginning and near the end of 98 dialysis sessions during which 28 morbid events were identified. In 10 of these sessions, where morbid events took place within 30 minutes of the measurements, CBV appeared to be a more sensitive indicator of morbid events than CO. We conclude that CO and CBV can be routinely and reliably measured during hemodialysis if precautions are taken to avoid specifically identified sources of error. Preliminary studies suggest that these measurements may have significant prognostic value.

Blood Volume↗
PubMed2000

[Knee endoprosthetic surgery: tasks and problems of the surgical instrument teams].

About 220 knee endoprostheses are implanted at our clinic annually. This is a routine procedure for the instrument staff. Practice has shown, however, that deficient operating room management as regards the instruments, implants, operating room staff, and surgical planning causes problems. As a result of this, a prophylactic search for sources of error began (risk management). If the sources of error are found, described, and remedied, knee endoprosthetic surgery will be successful for both the patient and the surgical team. Cooperation and communication among manufacturer, surgeon, and surgical nursing staff should serve to minimize forensic risks. The most important task of the instrument staff is to produce adequate structure and procedural quality so that a positive result can be achieved.

Arthroplasty, Replacement, Knee↗
PubMed2006

The promise and perils of microarray analysis.

Microarray analysis has provided a novel means of identifying clues into the mechanisms of disease development. As a methodology, microarray analysis holds the promise for genome-wide screening in which 2 tissues (diseased and normal) are compared, and molecular pathways that defined the phenotype of the disease could be precisely defined. Alternatively, microarray experiments can be used to differentially compare pathologically similar diseased tissues to predict response to chemotherapy and risk of recurrence. However, the clinician should be aware that various sources of error can influence microarray analysis results. Sources of error can be minimized but not eliminated, explaining why meticulously conducted experiments in different laboratories or using different platforms result in different lists of genes. Confirmation and validation of genome-wide microarray results using ancillary methods remains a critical step. With proper confirmatory studies and cautious interpretation, microarray analysis represents a powerful tool for molecular discovery.

Female↗
PubMed1995

Localisation of epileptic foci with multichannel magnetoencephalography, MEG.

With the development of multichannel magnetoencephalographs biomagnetic signals can be recorded over large areas at the same time. It allows determination of the magnetic field outside the head generated by spontaneous epileptic discharges. From the maxima of outward and inward magnetic fluxes the locations of the sources of epileptic discharges can be calculated. The biomagnetic signals originating from an epileptic discharge is, however, mixed with biomagnetic signals generated by the background activity of the brain. A localisation based on a single discharge will therefore be influenced by the background activity. To diminish this influence, the biomagnetic signals during repeated identical epileptic discharges have been averaged. It gives a source localisation common to all discharges instead of a widely spread cluster of dipole sources. The error of epileptic dipole source localisations varies with the site of the dipole in the head as judged from studies with implanted dipole sources but also with the direction of the dipole as seen in studies with artificial dipoles in real head volumes. The error is relatively small in areas where the head has a spherical surface if the dipole direction is tangential. At other sites or dipole directions, the error can be very large. Since the site and direction of an epileptic dipole source is unknown it is not possible to estimate the error of localisations except by using models of individual head volumes.

Artifacts↗
PubMed1983

The analysis of errors in orthodontic measurements.

The sources of error in cephalometric measurement and their analyses are discussed. The importance of distinguishing bias and random errors is emphasized, and methods of control are discussed. Randomization of record measurement is one of the most important methods of avoiding bias, but it is rarely undertaken in cephalometric studies. Random errors are particularly important in the evaluation of individual radiographs, and a measurement that has a high error in relation to its total variability will be of little value in clinical assessment. In serial studies of facial change, the error variance is always a major part of the total variance and thus results have to be interpreted with caution. In cross-sectional studies it is not possible to specify exactly the acceptable limits of random errors, because this will depend on the difference between groups that would be of interest and on the number of cases. The judicious replication of measurements can be important in the control of random errors. In many papers, adequate error evaluation and control is lacking. In these circumstances, the results are of limited value because it is not possible to tell whether an apparent effect is the result of bias in measurement or whether a real effect is being obscured by random errors. It is incumbent on authors to consider how their measurement errors should affect the interpretation of results.

Cephalometry↗
PubMed1985

Physician and coding errors in patient records.

The Veterans Administration's discharge abstract system was studied to identify error frequency, source, and effect in five Veterans Administration hospitals. We reviewed 1,829 medical records from 21 services for concordance with the abstract; sampling provided 95% confidence for each service. Of these records, 1,499 (82%) differed from the abstract in at least one item. Of 20,260 items, 4,360 (22%) were incorrect, with three error sources: physician (62%), coding (35%), and keypunch (3%). We projected 2.14 physician and 0.81 coding errors in the average abstract. Eighty-nine percent of projected physician errors were failures to report a procedure or diagnosis. Coding was subjective and errors were synergistic with physician errors. We projected that correction of errors would change 19% of the records for diagnosis-related group purposes and substantially increase future resource allocation. This effect varied considerably by service.

Abstracting and Indexing↗
PubMed1998

Bayesian estimates of error bounds for EEG source imaging.

Given a set of electrical potential measurements at the surface of the head, localizing the sources of the electrical activity is an inherently ill-posed problem. Bayesian methods can be used to specify prior information to constrain the possible source solutions. We show that Bayesian analysis can also provide a means for characterizing system noise levels, estimating the "error bars" surrounding source localization results, and estimating the information about brain processes conveyed by dense sensor array electroencephalographic (EEG) recordings. This method is, in principal, applicable to any linear model of EEG or magnetoencephalographic (MEG) processes. A series of simulations demonstrated the internal consistency of our method, the robustness to noise levels, and the limitations of accurate source localization with large numbers of sources.

Artifacts↗
PubMed1988

Estimation of energy expenditure, net carbohydrate utilization, and net fat oxidation and synthesis by indirect calorimetry: evaluation of errors with special reference to the detailed composition of fuels.

Sources of error in the interpretation of respiratory data are evaluated and reviewed with special reference to the detailed composition of foods. Estimates of fuel utilization or synthesis are 12-fold more sensitive to errors in the nonprotein respiratory quotient than is the heat equivalent of oxygen. Estimates of protein oxidation from nitrogen excretion can be in error from +14 to -39% of the true value. Heat equivalents of oxygen, respiratory quotients, and urinary nitrogen-to-oxygen conversion ratios are considered for 60 artificial and 101 conventional food proteins, 36 artificial and 125 conventional food fats, and the different carbohydrates contained in these foods. It is concluded that there is considerable uncertainty when the mix of fuels utilized is assessed accurately. Accuracy is best within 5% of the true values. This analysis is completed with descriptions of some physiological sources of error in an appendix.

Algorithms↗
PubMed1999

[Errors in blood pressure measuring with modern automated machines. Effects of errors in non-invasive oscillometric blood pressure measuring].

Automatic blood pressure measuring devices with digital display are now in common use, both among lay persons and physicians. The oscillometric method is, however, associated with a number of possible sources of error which, among other things, make comparison with the standard Riva-Rocci method difficult. Methodological errors arise from physiological/anatomical variations: circumference of the forearm and wrist, position of the arteries, structure of the surrounding tissue, arterial diameter and also vasomotor function. The latter represents an appreciable uncertainty factor, in particular with measurements obtained from the finger. Technological sources of error play a role in pronounced hypotension or severe hypertension, since the devices are calibrated only for a range extending from 120 to 180 mmHg. The processing by the device of arrhythmic pulses is also critical. Additional sources of error are in handling and interpretation. Overall, these sources of error are such that not all the various types of device available are equally suitable for use by the patient, and it is necessary to place limitations on the application of such devices and to establish rules for their use.

Arm↗
PubMed1999

Permanent implantation of 125I sources in the prostate: radical limits of simplicity.

PURPOSE: To determine the effect of reducing the number of sources per implantation on the dose coverage of the prostate volume. MATERIALS AND METHODS: Idealized source distributions were planned for four, eight, 16, 24, 32, and 48 sources. The peripheral loading technique was used to plan a uniform, conformal dose distribution to the target volume, which was the prostate volume as visualized at ultrasonography. Source-placement error was estimated by using measured error magnitudes and was expressed with systematic and random components. The relative sensitivities of the plans to the source-placement error were studied. RESULTS: Idealized planned target coverage can be adequately achieved with comparable dose distributions with eight or more sources. The sensitivity to source-placement error is comparable for plans with 16 or more sources. CONCLUSION: It is theoretically possible to radically simplify implantation without compromising target coverage or error tolerance.

Brachytherapy↗
PubMed2001

Sampling optimization, at site scale, in contamination monitoring with moss, pine and oak.

With the aim of optimizing protocols for sampling moss, pine and oak for biomonitoring of atmospheric contamination and also for inclusion in an Environmental Specimen Bank, 50 sampling units of each species were collected from the study area for individual analysis. Levels of Ca, Cu, Fe, Hg, Ni, and Zn in the plants were determined and the distributions of the concentrations studied. In moss samples, the concentrations of Cu, Ni and Zn, considered to be trace pollutants in this species, showed highly variable long-normal distributions; in pine and oak samples only Ni concentrations were log-normally distributed. In addition to analytical error, the two main source of error found to be associated with making a collective sample were: (1) not carrying out measurements on individual sampling units; and (2) the number of sampling units collected and the corresponding sources of variation (microspatial, age and interindividual). We recommend that a minimum of 30 sampling units are collected when contamination is suspected.

Air Pollutants↗
PubMed2004

Uncertainty in estimates of HIV/AIDS: the estimation and application of plausibility bounds.

OBJECTIVES: To establish the accuracy of the country specific estimates of HIV prevalence, incidence, and AIDS mortality published every 2 years by UNAIDS and WHO. METHODS: We review sources of error in the data used to generate national HIV/AIDS and where possible estimate their statistical properties. We use numerical and approximate analytic methods to estimate the combined impact of these errors on HIV/AIDS estimates. Heuristic rules are then derived to produce plausible bounds about these estimates for countries with different types of epidemic and different qualities of surveillance system. RESULTS: Although 95% confidence intervals (CIs) can be estimated for some sources of error, the sizes of other sources of error must be based on expert judgment. We therefore produce plausible bounds about HIV/AIDS estimates rather than statistical CIs. The magnitude of these bounds depends on the stage of the epidemic and the quality and coverage of the sentinel HIV surveillance system. The bounds for adult estimates are narrower than those for children, and those for prevalence are narrower than those for new infections. CONCLUSIONS: This paper presents a first attempt at a rigorous description of the errors associated with estimation of global statistics of an infectious disease. The proposed methods work well in countries with generalised epidemics (>1% adult HIV prevalence) where the quality of surveillance is good. Although methods have also been derived for countries with low level or concentrated epidemics, more data on the biases in the estimation process are required.

Acquired Immunodeficiency Syndrome↗
PubMed1994

Finding the depth of magnetic brain stimulation: a re-evaluation.

The depth of threshold magnetic nerve stimulation can be estimated by using thresholds from two different-sized stimulus coils and plotting their induced electric field vs. depth profiles. Stimulation is presumed to take place where the two field profiles are equal. If the two coils have unequal inductances, however, there is a relative shift in threshold between coils that alters the intersection point and the apparent stimulus depth. This systematic error arises from two sources: (1) there is a difference in the fraction of stimulator energy reaching each coil, and (2) pulse durations are different, causing threshold shifts governed by the nerve strength-duration curve. Both sources of error are additive. If the larger coil has the lesser inductance, stimulus depth is underestimated; if it has the greater inductance, it is overestimated. This can lead to large disparities in the measured depth, depending on the sets of coils used. In this paper, we show how to correct for errors introduced by unequal inductance and how this resolves discrepancies in depth measurement. Our own depth measurements in the motor area for threshold finger movements, and recalculated depths from Epstein et al., indicate that stimulation is slightly deeper (18-21 mm, average 19+ mm) than previously thought. This suggests that threshold magnetic stimulation in the motor area may arise from large, tangentially oriented fibers in the superficial white matter, or in the gray matter at the upper sulcus or lip of the gyrus.

Adult↗
PubMedDate not supplied

Eliminating errors in emergency medical services: realities and recommendations.

Errors in health care can have serious consequences, not only for patients but for society as a whole, given the considerable national expenditures required to address these errors. Because of the number of patients treated and the acuity of emergency situations, eliminating errors should be a priority in emergency medical services (EMS) systems. In a recent report, the Institute of Medicine called for improvements in patient safety, which it defined as freedom from accidental injury. Recent efforts have focused on integrating EMS systems into error analyses of the total health care system. However, EMS systems must take the initiative in addressing their own major error-prone areas using the best and most current data available. Unfortunately, addressing the problem of medical errors in EMS systems still suffers from a paucity of data, owing to a lack of organized, funded programs backed by legislation and dedicated government coordination. We recommend that EMS medical directors consider specific error audits to decrease sources of errors and to be better able to identify EMS providers who would benefit from retraining. Error audits might first be focused on the following potentially serious errors: equipment malfunction, failure to check oxygen saturation, failure to immobilize the patient, use of incorrect protocol or algorithm, failure to check glucose levels, failure to recognize patient deterioration, failure to detect misplaced endotracheal tubes, and use of wrong drug or drug dose.

Emergency Medical Services↗
PubMed2005

Statistical bias in 3-D reconstruction from a monocular video.

The present state-of-the-art in computing the error statistics in three-dimensional (3-D) reconstruction from video concentrates on estimating the error covariance. A different source of error which has not received much attention is the fact that the reconstruction estimates are often significantly statistically biased. In this paper, we derive a precise expression for the bias in the depth estimate, based on the continuous (differentiable) version of structure from motion (SfM). Many SfM algorithms, or certain portions of them, can be posed in a linear least-squares (LS) framework Ax = b. Examples include initialization procedures for bundle adjustment or algorithms that alternately estimate depth and camera motion. It is a well-known fact that the LS estimate is biased if the system matrix A is noisy. In SfM, the matrix A contains point correspondences, which are always difficult to obtain precisely; thus, it is expected that the structure and motion estimates in such a formulation of the problem would be biased. Existing results on the minimum achievable variance of the SfM estimator are extended by deriving a generalized Cramer-Rao lower bound. A detailed analysis of the effect of various camera motion parameters on the bias is presented. We conclude by presenting the effect of bias compensation on reconstructing 3-D face models from rendered images.

Algorithms↗
PubMed2006

Space-time relativity in self-motion reproduction.

Experiments on reproducing imposed self-motion showed that not only final distance or angle of motion, but also the temporal profile are reproduced. Reproduction errors have been attributed to sensory inputs, inaccurate memorization of the motion variable, or motor errors. However, another possible source of error has so far been neglected. The internal time base for path integration or movement memorization may be distorted and thus not reflect physical time. Because additional cognitive load was previously shown to affect subjective estimation of duration, we used a dual-task paradigm during either the stimulation or reproduction phase of three different movement reproduction tasks. We asked subjects 1) on a rotating chair to reproduce imposed passive whole body rotations by controlling the chair with a joystick, 2) on a treadmill to actively reproduce locomotion with respect to the treadmill, and 3) while blindfolded to reproduce a previously walked straight trajectory. The cognitive load changed the distance of reproduced self-motion by about 25% depending on whether the mental task was performed while experiencing or reproducing the motion. Although imposed velocity was reproduced accurately in all conditions, reproduced movement duration was affected in the same way as distance. This result implies that for the perception of distance traveled, perceptual space and time are closely interrelated. The findings are consistent with shared processing of temporal and spatial information. A computational model of motion reproduction including a discrete path integrator is proposed that is able to explain the experimental results within one coherent framework.

Adult↗