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At least 1,657 records · Page 92Linked to original sources
PubMed1989

A three-dimensional musculoskeletal model for gait analysis. Anatomical variability estimates.

Three-dimensional coordinates defining the origin and insertion of 40 muscle units, and bony landmarks for osteometric scaling were identified on dry bone specimens. Interspecimen coordinate differences along the anterior-posterior axis of the pelvis and the long bone axes of the pelvis, femur and leg were reduced by scaling but landmark differences along the other axes were not. The coordinates were mapped to living subjects using close-range photogrammetry to locate superficial reference markers. The error of predicting the positions of internal coordinates was assessed by comparing joint centre locations calculated from local axes defining the orientation of segments superior and inferior to a joint. A difference was attributed to: anatomical variability not accounted for by scaling; errors in identifying and placing reference landmarks; the accuracy of locating markers using photogrammetry and error introduced by marker oscillation during movement. Anatomical differences between specimens are one source of error in defining a musculoskeletal model but larger errors are introduced when such models are mapped to living subjects.

Anthropometry↗
PubMed2000

Methods for measuring ethane and pentane in expired air from rats and humans.

Numerous studies in animals and humans provide evidence that ethane and pentane in expired air are useful markers of in vivo lipid peroxidation. The measurement of breath hydrocarbons, being noninvasive, is well suited for routine use in research and clinical settings. However, the lack of standardized methods for collecting, processing, and analyzing expired air has resulted in the use of a wide variety of different methods that have yielded highly disparate results among investigators. This review outlines the methods that we have developed and validated for measuring ethane and pentane in expired air from rats and humans. We describe the advantages of these methods, their performance, as well as potential errors that can be introduced during sample collection, concentration, and analysis. A main source of error involves contamination with ambient-air ethane and pentane, the concentrations of which are usually much greater and more variable than those in expired air. Thus, it appears that the effective removal of ambient-air hydrocarbons from the subject's lungs before collection is an important step in standardizing the collection procedure. Also discussed is whether ethane or pentane is a better marker of in vivo lipid peroxidation.

Animals↗
PubMed2006

The performance of semilocal and hybrid density functionals in 3d transition-metal chemistry.

We investigate the performance of contemporary semilocal and hybrid density functionals for bond energetics, structures, dipole moments, and harmonic frequencies of 3d transition-metal (TM) compounds by comparison with gas-phase experiments. Special attention is given to the nonempirical metageneralized gradient approximation (meta-GGA) of Tao, Perdew, Staroverov, and Scuseria (TPSS) [Phys. Rev. Lett. 91, 146401 (2003)], which has been implemented in TURBOMOLE for the present work. Trends and error patterns for classes of homologous compounds are analyzed, including dimers, monohydrides, mononitrides, monoxides, monofluorides, polyatomic oxides and halogenides, carbonyls, and complexes with organic pi ligands such as benzene and cyclopentadienyl. Weakly bound systems such as Ca(2), Mn(2), and Zn(2) are discussed. We propose a reference set of reaction energies for benchmark purposes. Our all-electron results with quadruple zeta valence basis sets validate semilocal density-functional theory as the workhorse of computational TM chemistry. Typical errors in bond energies are substantially larger than in (organic) main group chemistry, however. The Becke-Perdew'86 [Phys. Rev. A 38, 3098 (1988); Phys. Rev. B 33, 8822 (1986)] GGA and the TPSS meta-GGA have the best price/performance ratio, while the TPSS hybrid functional achieves a slightly lower mean absolute error in bond energies. The popular Becke three-parameter hybrid B3LYP underbinds significantly and tends to overestimate bond distances; we give a possible explanation for this. We further show that hybrid mixing does not reduce the width of the error distribution on our reference set. The error of a functional for the s-d transfer energy of a TM atom does not predict its error for TM bond energies and bond lengths. For semilocal functionals, self-interaction error in one- and three-electron bonds appears to be a major source of error in TM reaction energies. Nevertheless, TPSS predicts the correct ground-state symmetry in the vast majority of cases and rarely fails qualitatively. This further confirms TPSS as a general purpose functional that works throughout the periodic table. We also give workstation timing comparisons for the 645-atom protein crambin.

Journal Article↗
PubMed2003

Seabed reflection measurement uncertainty.

The seabed reflection coefficient is a fundamental property of the ocean waveguide. Measurements of the frequency and angular dependence of the reflection coefficient can provide information about the geoacoustic properties of the seabed or can be used as an input to propagation models. The uncertainty of the measurements must be known in order to determine prediction uncertainties for the acoustic field and/or the geoacoustic properties. Analysis indicates that the reflection measurements have a standard deviation from +/- 0.5-1 dB at full angular resolution depending on frequency and experiment geometry. The dominant contribution to the error is source amplitude variability, and a new processing approach was developed that reduces the error for frequencies above a few hundred Hz. Further reduction in the uncertainty can be obtained by averaging in angle, for example, a +/- 1 degrees angle averaging leads to a standard deviation of less than +/- 0.5 dB. Errors in the angle estimate are a few tenths of a degree from 0-34 degrees grazing angle: the crucial angular range for predicting long-range propagation or for geoacoustic property inversion.

Journal Article↗
PubMed1982

Errors due to data reduction in single-breath method for measurement of pulmonary blood flow.

The validity and precision of the single-breath method for determination of pulmonary blood flow suggested by Kim et al. (J. Appl. Physiol. 21: 1338-1344, 1966) have been estimated by a number of workers with very different results. The present work is an analysis of the errors that arise solely due to the data-reduction procedure used to calculate the pulmonary blood flow from the primary data. The analysis, which consists of a computer simulation of the system, shows that very considerable errors may arise from the data-reduction procedure itself and that these errors are very sensitive to small differences in the experimental design. The basic source of errors in the data-reduction procedure seems to be the use of a fitted polynomial to computer derivatives of a nonpolynomial experimental curve. Finally, the analysis suggests a design in which the errors would be quantitatively insignificant.

Carbon Dioxide↗
PubMed1992

[Competence sharing between health insurance and medical service].

The borderlines between the areas of competence of the German compulsory health insurance authorities and their Medical Service can be drawn as follows: 1. The German compulsory health insurance body is legally obliged to clarify the facts concerning a patient and his illness. It is therefore imperative for the health insurance body to prepare the ground in each individual case in such a manner that the case in question can be entrusted to a doctor called upon to write an expertise, but the final decision in respect of the insurance coverage rests exclusively with the health insurance body. 2. The Medical Service system is component for helping to find the fact that must be known before the administrative procedure to arrive at a decision is initiated. The expertise given by the Medical Service is a decision help invaluably important on the grounds of specialist knowledge, knowledge of facts and experience gathered from medical practice. Wherever the borderlines of such competencies are overstepped, there is a risk of errors occurring in the expertise and in the administrative decisions based thereon. Such sources of error can be eliminated only if both parties know and accept their limitations and also do not expect the other side to cross these boundaries.

Disability Evaluation↗
PubMed2002

Source monitoring impairments in schizophrenia: characterisation and associations with positive and negative symptomatology.

This article describes a consistent pattern of the associations between source monitoring failure and clinical symptomatology in schizophrenia. The associations with positive symptoms in this sample have been reported previously, but not the associations with negative symptoms. Forty patients with schizophrenia were administered several memory tasks including free recall of lists of words, recognition and source memory. Various memory errors assumed to stem from source monitoring failure were derived. They include intrusions and recall of words from previous lists in free recall, false recognitions, and confusion with regard to the source of the stimuli. We studied the associations of these memory errors with positive symptoms and with a broad range of negative symptoms. All the memory errors were positively associated with at least one positive symptom. On the other hand, these errors were inversely associated with certain negative symptoms reflecting lack of emotion or lack of social interactions. Thus positive and negative symptomatology appear to have opposite links to the source monitoring errors observed in patients with schizophrenia. Cognitive mechanisms leading to different types of source monitoring errors and possibly to the formation of positive symptoms are discussed.

Adult↗
PubMed2005

Modeling error variance in job specification ratings: the influence of rater, job, and organization-level factors.

The authors modeled sources of error variance in job specification ratings collected from 3 levels of raters across 5 organizations (N=381). Variance components models were used to estimate the variance in ratings attributable to true score (variance between knowledge, skills, abilities, and other characteristics [KSAOs]) and error (KSAO-by-rater and residual variance). Subsequent models partitioned error variance into components related to the organization, position level, and demographic characteristics of the raters. Analyses revealed that the differential ordering of KSAOs by raters was not a function of these characteristics but rather was due to unexplained rating differences among the raters. The implications of these results for job specification and validity transportability are discussed.

Adult↗
PubMed2000

Estimation of projection errors in human ocular fundus imaging.

Photogrammetric analysis of features in human ocular fundus images is affected by various sources of errors, for example aberrations of the camera and eye optics. Another--usually disregarded--type of distortion arises from projecting the near spherical shape of the fundus onto a planar imaging device. In this paper we quantify such projection errors based on geometrical analysis of the reduced model eye imaged by a pinhole camera. The projection error found near the edge of a 50 degrees fundus image is 24%. In addition, the influence of axial ametropia is investigated for both myopia and hyperopia. The projection errors found in hyperopia are similar to those in emmetropia, but decrease in myopia. Spherical as well as ellipsoidal eye shapes were used in the above calculation and their effect was compared. Our results suggest that the simple spherical eye shape is sufficient for correcting projection distortions within a range of ametropia from -5 to +5 diopters.

Artifacts↗
PubMed2003

Implementation of error-processing in the human anterior cingulate cortex: a source analysis of the magnetic equivalent of the error-related negativity.

Recent research has described a component of human electrical brain activity (the ERN or NE) that is associated with error-processing. In the present experiment, we used magneto-encephalographic recordings to provide converging evidence both for the existence of this component and for its putative source in the brain. Six human subjects performed a Go-NoGo task while both magnetoencephalographic and electroencephalographic brain activity were recorded. We found evidence for a magnetic equivalent of the ERN and dipole source analysis suggested that this activity was generated in the anterior cingulate cortex. These data converge with those from electrical recordings in implicating this brain structure in error-processing.

Adult↗
PubMed2004

Musculoskeletal responses of 2-year-old Thoroughbred horses to early training. 2. Measurement error and effect of training stage on the relationship between objective and subjective criteria of training workload.

AIM: To identify the magnitude and sources of error involved in simply quantifying the workload of a group of Thoroughbred racehorses in training. METHODS: Data were obtained from seven 2-year-old fillies trained for 13 weeks on sand and grass tracks at various cantering velocities, and at the gallop in the last 4 weeks. Four fillies completed training and comprised a 'high exercise intensity' subgroup; three fillies did not complete all gallops due to lameness or injury and comprised a 'medium exercise intensity' subgroup. The trainer recorded the distance, time, track used, and subjective gait (SG; viz canter, 1/4-pace, 1/2-pace and gallop) of each horse each day. Data were analysed to describe the training programme and sources of variation in workload. A cumulative workload index (CWI) was devised to simply express distance and velocity aspects of the training programme. RESULTS: The magnitude of errors in measurement of timing and distance were small but significant (<0.8%, p=0.01). SG was an inaccurate descriptor of velocity. Mean velocity of 1/2-pace decreased from 8.92 (SE 0.049) in Weeks 6-8 to 6.33 (SE 0.061) m/sec after the start of galloping sessions in Week 9 (p=0.01). Track surface had a significant effect on the velocity of 1/2-pace (p=0.001). The fastest velocity was recorded on the grass (9.06, SE 0.292 m/sec), followed by 'plough' (8.23, SE 0.152 m/sec), and sand (7.90, SE 0.132 m/sec) tracks. The CWI of the horses ranged between 1,085,000 and 1,634,000 (mean=1,428,000; SE 78,000). The average exercise intensity per week was 110,000 (SE 1,048). There were no significant differences between high and medium exercise intensity subgroups for the canter and 1/4-pace. The high exercise subgroup had a greater CWI for the 1/2-pace (839,000 vs 559,000; p=0.004), gallop (71,000 vs 31,000; p=0.001), and total index (1,580,000 vs 1,242,000; p=0.001). CONCLUSIONS: The workload history of a horse can be accurately described using an index based on manual measurement of the time and distance worked. CLINICAL RELEVANCE: Accurate and precise data on the training programme of performance horses are likely to enable greater differentiation of aspects of workload which are associated with both performance and injury.

Journal Article↗
PubMedDate not supplied

Impact of marrow fat on accuracy of quantitative CT.

An assessment of the role of marrow fat as a source of error in single energy quantitative CT (SEQCT) measurements of the spine is presented. Fat-induced shifts and spreads in SEQCT findings are discriminated and quantified. Studies using chemical analysis have reported an average vertebral bone mineral (MIN) loss of approximately 1.3 mg/ml (0.9%) per year from a peak MIN of 150 mg/ml at age 30 years with a standard error of the estimate (SEE) of approximately 23 mg/ml [coefficient of variation (CV) = 20%]; intraosseous vertebral fat content increases by approximately 2.4 mg/ml (1.4%) per year from a fat density of 175 mg/ml at age 30 years with an SEE of approximately 87.5 mg/ml (CV = 36%). If one does not adjust for the average age-related fat change, SEQCT underestimates MIN and overestimates MIN loss by 10-30% (at a scanner setting of approximately 80 kVp). Application of correction procedures reduces the average underestimation to 1-3%. The impact of residual vertebral fat variability on the accuracy of MIN measurements accounts for only 12-24% of the total accuracy error of typically 10-15 mg/ml. The impact of fat changes between zero and twice the normal age-related rate on MIN loss measurements on individual patients and patient groups (treatment versus control) accounts for only 1-2% of the total precision error of typically 1.5-3 mg/ml. From 94 to 99% of the spread of SEQCT versus age data is caused by sources of variability other than fat. All fat-related errors are higher than the above estimates by a factor of approximately 1.5-2.5 when scanning at higher voltages of up to 130 kVp. Given the limited impact of fat variability, we conclude that for most clinical applications, MIN and bone loss measurements should use SEQCT. Adjustment for the average under/overestimation (by either explicitly correcting SEQCT findings or by comparing them with normative data obtained on a similar scanner), measuring at low voltages of approximately 80 kVp, and strict compliance to quality assurance procedures are highly recommended to achieve optimum accuracy.

Adipose Tissue↗
PubMed1979

Possibility for error in FDA diffusion assays.

Computational procedures specified for the FDA single-dose diffusion assay for antibiotics may cause substantial error in estimated sample potency. An unrecognized mistake in reference solution concentration is the source of error. It is caused by correcting responses from standard and sample plates differently. The error can be avoided by correcting both standard and sample responses to the observed reference response.

Anti-Bacterial Agents↗
PubMed2002

Principles and techniques of blood pressure measurement.

The gold standard for clinical blood pressure measurement continues to be readings taken by a physician using a mercury sphygmomanometer, but this is changing as mercury is gradually being phased out. The oscillometric technique, which primarily detects mean arterial pressure, is increasingly popular for use in electronic devices. Other methods include ultrasound (used mainly to detect systolic pressure) and the finger cuff method of Penaz, which can record beat-to-beat pressure noninvasively from the finger. The preferred location of measurement is the upper arm, but errors may occur because of changes in the position of the arm. Other technical sources of error include inappropriate cuff size and too rapid deflation of the cuff. Clinic readings may be unrepresentative of the patient's true blood pressure because of the white coat effect, which is defined as the difference between the clinic readings and the average daytime blood pressure. Patients with elevated clinic pressure and normal daytime pressure are said to have white coat hypertension. There are three commonly used methods for measuring blood pressure for clinical purposes: clinic readings, self-monitoring by the patient at home, and 24-hour ambulatory readings. Self-monitoring is growing rapidly in popularity and is generally carried out using electronic devices that work on the oscillometric technique. Although standard validation protocols exist, many devices on the market have not been tested for accuracy. Such devices can record blood pressure from the upper arm, wrist, or finger, but the arm is preferred. Twenty-four-hour ambulatory monitoring has been found to be the best predictor of cardiovascular risk in the individual patient and is the only technique that can describe the diurnal rhythm of blood pressure accurately. Ambulatory monitoring is mainly used for diagnosing hypertension, whereas self-monitoring is used for following the response to treatment. Different techniques of blood pressure measurement may be preferred in certain situations. In infants the ultrasound technique is best, whereas in pregnancy and after exercise the diastolic pressure may be hard to measure using the conventional auscultatory method. In obese subjects it is important to use a cuff of the correct size.

Age Factors↗
PubMed2006

Comment on "Computational improvements reveal great bacterial diversity and high metal toxicity in soil".

Gans et al. (Reports, 26 August 2005, p. 1387) provided an estimate of soil bacterial species richness two orders of magnitude greater than previously reported values. Using a re-derived mathematical model, we reanalyzed the data and found that the statistical error exceeds the estimate by a factor of 26. We also note two potential sources of error in the experimental data collection and measurement procedures.

Bacteria↗
PubMed1997

Pitfalls in epidemiological analysis.

Epidemiologists rely heavily on the relative risk in their analyses and presentations. As an index it is intelligible and intuitively appealing but can give an exaggerated impression of the strength of the association and is unreliable for comparisons. This can be shown by deriving relative risks from a normal correlation surface with an unimpressive level of correlation. Relative risks ought to be handled with caution; the underlying population risk and the relative size of exposed and reference categories should be reported. Efforts to control for additional variables, confounders, by some kind of multi-variate technique, another standard procedure, could easily give a false sense of security. From time to time it has been made clear in the literature that errors of measurement in the third variable or in the additional variables could lead to the appearance of false independent effects, but these warnings do not seem to have been heeded nearly as much as they deserve. A simulation experiment is used to bring the lesson home, with realistic numerical assumptions. A moderate degree of error contamination will produce spurious effects. This has nothing to do with sampling errors, large samples rather aggravate this danger. In meta-studies this is a source of error and conflicting results to take account of.

Confounding Factors, Epidemiologic↗
PubMed1966

Discriminative echolocation in a porpoise.

Operant conditioning techniques were used to establish a discriminative echolocation performance in a porpoise. Pairs of spheres of disparate diameters were presented in an under-water display, and the positions of the spheres were switched according to a scrambled sequence while the blindfolded porpoise responded on a pair of submerged response levers. Responses which identified the momentary state of the display were food-reinforced, while those which did not (errors) produced time out. Errors were then studied in relation to decreased disparity between the spheres. As disparity was decreased, errors which terminated runs of correct responses occurred more frequently and were followed by longer strings of consecutive errors. Increased errors and disruption of a stable pattern of collateral behavior were associated. Since some sources of error other than decreased disparity were present, the porpoise's final performance did not fully reflect the acuity of its echolocation channel.

Animals↗