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At least 1,189 records · Page 66Linked to original sources
PubMed2006

Discrimination of errors from neuronal activity in functional MRI of the human spinal cord by means of general linear model analysis.

Functional MRI (fMRI) of the spinal cord has been demonstrated to provide reliable and sensitive maps of neuronal activity, particularly when combined across several experiments. Individual experiments reveal neuronal activity as well as errors. The dominant source of errors is hypothesized to be physiological motion, including cardiac and respiratory motion, flow of blood and cerebrospinal fluid (CSF), and motion of the spinal cord within the spinal canal. All of the hypothesized sources of error are therefore related to cardiac and respiratory motion, which can be recorded during an fMRI experiment. Analyses were carried out with a general linear model (GLM) with peripheral pulse and respiration recordings used as models of errors. The results demonstrate that the sensitivity of spinal fMRI is improved and errors are reduced when peripheral pulse traces are used in the GLM, but no improvement was detected with the inclusion of respiratory traces.

Humans↗
PubMedDate not supplied

Value of duplicate smears in cervical cytology.

The cytologic accuracy, sources of error and value of duplicate samples were studied in 87 women simultaneously biopsied for cervical intraepithelial neoplasia. Separately evaluated by two laboratories, correlation with biopsy was 70% for the first cytology and 67% for the second. Discrepant cytologies were reciprocally reviewed in error analysis. The sources of error were cytologic sampling (10.9%), evaluation (5.8%) and both (4.0%). Attention is directed to the high proportion of cases (15%) in which sampling error was a factor; awareness of this observation is necessary in patient management. The duplicate second cytology was of substantial value in 7% of the cases and helpful in an additional 3.5%; both figures are lower than in recent reports. If errors in evaluation or evaluation sampling are held to a 10% level, routine duplicate studies may not be justified.

Carcinoma in Situ↗
PubMed2003

Beyond alpha: an empirical examination of the effects of different sources of measurement error on reliability estimates for measures of individual differences constructs.

On the basis of an empirical study of measures of constructs from the cognitive domain, the personality domain, and the domain of affective traits, the authors of this study examine the implications of transient measurement error for the measurement of frequently studied individual differences variables. The authors clarify relevant reliability concepts as they relate to transient error and present a procedure for estimating the coefficient of equivalence and stability (L. J. Cronbach, 1947), the only classical reliability coefficient that assesses all 3 major sources of measurement error (random response, transient, and specific factor errors). The authors conclude that transient error exists in all 3 trait domains and is especially large in the domain of affective traits. Their findings indicate that the nearly universal use of the coefficient of equivalence (Cronbach's alpha; L. J. Cronbach, 1951), which fails to assess transient error, leads to overestimates of reliability and undercorrections for biases due to measurement error.

Bias↗
PubMed1998

Wrist arthrography after acute trauma to the distal radius: diagnostic accuracy, technique, and sources of diagnostic errors.

RATIONALE AND OBJECTIVES: The objective of this investigation was to determine the diagnostic accuracy of wrist arthrography in the detection of interosseous ligament disruptions and of triangular fibrocartilage complex (TFCC) lesions in patients after acute wrist trauma and to define the sources of diagnostic error of wrist arthrography after recent trauma. METHODS: Twenty-two patients with radial fractures after acute wrist trauma underwent arthrography and arthroscopy of the wrist. Arthrography was performed in a standardized manner by two- or three-compartment injection technique. Subsequently wrist arthroscopy was performed within the same session. Image analysis included the evaluation of interosseous carpal ligaments, the TFCC, and the osseous structures. RESULTS: In 22 patients, 11 injuries of the intrinsic ligaments and the TFCC were diagnosed by arthroscopy, of which 9 had been diagnosed correctly with arthrography before surgery. One scaphoid fracture previously missed on conventional radiographs also could be diagnosed by arthrography. CONCLUSION: Arthrography of the posttraumatic wrist is a valuable tool in the diagnostic evaluation of interosseous carpal ligaments and the TFCC.

Adult↗
PubMed1998

Medication errors in paediatric practice: insights from a continuous quality improvement approach.

UNLABELLED: The objective was to assess the incidence and consequences of medication errors, highlight sources of recurrent error and institute changes in practice to prevent their recurrence. Utilising a continuous quality improvement approach, a 2-year prospective cohort study was undertaken using an adverse incident reporting scheme. A multidisciplinary committee analysed medication error reports, classifying them according to type (prescription, supply or administration), severity (serious or not serious) and clinical outcome. Changes in policy and practice were implemented to reduce the frequency of errors. There were 441 reported medication errors in the study period, during which 682 patients were admitted for 5315 inpatient days. Errors were more seven times likely to occur in the intensive care setting. Doctors accounted for 72% of errors and prescription errors doubled when new doctors joined the rotation. Most errors (68%) were detected prior to drug administration. Twenty-four serious medication errors were not detected in advance, but only 4 had overt clinical consequences. Excluding prevented errors and appropriate deviations from prescribed therapy, there were 117 actual medication errors (1/5.8 admissions, or 1/45 inpatient days). During the 2nd year of the scheme, the incidence of all reported errors, administration errors and serious errors fell, but the prescription error rate remained constant. CONCLUSIONS: Medication errors occurred commonly in this study, but adverse consequences were rare. The non-punitive, multidisciplinary approach to medication errors utilised in this study increased staff vigilance, highlighted sources of recurrent error, and led to changes in drug policies and staff training, which resulted in improved patient safety and quality of care.

Cohort Studies↗
PubMed2004

Exploring variability and sources of measurement error in alcohol expectancy questionnaire reliability coefficients: a meta-analytic reliability generalization study.

OBJECTIVE: Reliability Generalization, a relatively new meta-analytic score reliability technique, was used to examine reliability coefficients for Alcohol Expectancy Questionnaire (AEQ) subscales in published research. Specifically, the present study identified the typical reliability coefficients of scores on AEQ subscales across published studies and examined sources of measurement error across AEQ subscales and studies. METHOD: Based on literature reviews of PsyclNFO and PubMed, a total of 71 studies were analyzed and coded on 10 different dimensions believed to affect score reliability. RESULTS: Only 37% of the studies surveyed reported reliability coefficients for the data in hand. Analysis of these studies revealed that the average score reliability across studies varied considerably in subscales and samples, with the Arousal/Interpersonal Power and Sexual Enhancement subscales evidencing the greatest variability. Gender homogeneity and racial homogeneity were found to be the two most important predictors of the magnitude of score reliability coefficients across subscales and studies. CONCLUSIONS: Results of the study indicate that the AEQ tends to generate reliable scores, with some noted exceptions. Because the Arousal/Interpersonal Power and Sexual Enhancement subscales tend to generate unacceptably low reliability coefficients and because the AEQ holds promise in furthering prevention and treatment outcome research, it is suggested that future research with the AEQ explore instrument factor structure and item consistency. Because reliability estimates can influence substantive statistical analyses, it is recommended that authors using the AEQ report reliability information in their published work.

Alcohol Drinking↗
PubMed1987

The role of model and computational experiments in the biomagnetic inverse problem.

This is a review of the role of model and computational experiments in studies of the part of the biomagnetic inverse problem that deals with the determination of electrical sources in the body using magnetic measurements around the body. Results from modelling studies of the forward problem that are important for the inverse problem are also reviewed. An evaluation is made of the adequacy of various models of the body for use in the biomagnetic inverse problem. This evaluation indicates that simple torso models, e.g. a semi-infinite volume or sphere, are probably inadequate. The review of the modelling studies of the inverse problem includes the effects of noise, source modelling errors, body modelling errors and measurement errors on the accuracy of source localisation methods using magnetic measurements. Source modelling errors are caused by differences between an actual complex source in the body and the simple model of it used in most source localisation methods; body modelling errors are caused by differences between the actual body and a simple model of it. The review indicates that typical experimental noise will only cause significant source localisation errors for inverse solutions calculated using fewer than approximately ten measurement points; it also indicates that source modelling errors must be rather large to be detectable when typical experimental noise is present. In addition, the review indicates that many experimental measurement errors will not cause significant localisation errors. The effects of body modelling errors are largely unknown. Suggestions for further biomagnetic inverse problem research are given. These include the development of more realistic models of the body, the experimental verification of such models and source localisation methods, and the development of methods for detecting and localising distributed or multiple discrete sources.

Electric Conductivity↗
PubMed1983

Humidity as a source of measurement error in osteometrics.

A simple experiment was conducted to test the hypothesis that variation in humidity causes expansion of bone and, thereby, affects measurements of dried, preserved skulls. The experiment consisted of subjecting ten macaque skulls to increased humidity for 24 hours. Measurements of nine skull dimensions taken immediately before and after humidification revealed a statistically significant treatment effect of increased skull size with increased humidity. The length of the molar tooth row increased by about 0.1 mm (0.50%) while the greatest length of the skull increased by about 0.9 mm (0.57%). The specimens returned to their original dimensions within 1-2 days after being removed from the humidity chamber. These results confirm the impression gained by the practical experience of measuring museum specimens in different locations and environments. It appears that bony changes associated with humidity differences represent a real, though minor, source of measurement error in osteometrics.

Animals↗
PubMed1998

Measurement error as a source of QT dispersion: a computerised analysis.

OBJECTIVE: To establish a general method to estimate the measuring error in QT dispersion (QTD) determination, and to assess this error using a computer program for automated measurement of QTD. SUBJECTS: Measurements were done on 1220 standard simultaneous 12 lead electrocardiograms. DESIGN: The computer program was validated against two observers on a random subset of 100 electrocardiograms. Simple laws of physics require that at least five of the six extremity leads have the same QT duration. This allows the direct assessment of the error in measuring QTD derived from five extremity leads (QTD5). It also enables ST-T amplitude dependent distributions of measurement error in determining QT duration to be established. These QT error distributions were then used to estimate the error in measuring QTD from all 12 leads (QTD12). MAIN OUTCOME MEASURES: Mean and standard deviation of error in measuring QTD duration, QTD5, and QTD12. RESULTS: Performance of the program was comparable to that of observers. Errors in measuring QT duration (measured QT minus reference QT) fell from a mean (SD) of 6.9 (17.1) ms for ST-T amplitudes < 50 microV to -1.4 (6.3) ms for amplitudes > 350 microV. Measurement errors of QTD5 and QTD12 were 20.4 (11.5) ms and 29.4 (14.9) ms. CONCLUSIONS: The fact that no QTD can exist between five of the six extremity leads provides a means of estimating QTD measurement error. Measuring error of QT duration is dependent on ST-T amplitude. QTD measurement error is large compared with typical QTD values reported.

Databases, Factual↗
PubMed2001

Sources of preventable errors related to transfusion.

BACKGROUND AND OBJECTIVES: Transfusion errors always remain under-reported owing to a lack of awareness about transfusion-related adverse events among the hospital staff and an inadequate feedback system in most of the transfusion centres. This article reports the results obtained from a study carried out to investigate the sources and types of errors in our tertiary care hospital. MATERIALS AND METHODS: The errors reported by the blood bank staff (i.e. reception counter clerical and technical staff) and the residents in charge of the patient, were studied over a period of 1 year (from May 1998 to April 1999) and classified based on the site of occurrence. RESULTS: A total of 123 errors were detected over the 1-year study period. Of these 123 errors, 107 (86.99%) occurred outside the blood bank and 16 (13%) in the blood bank. CONCLUSION: Errors occur most frequently outside the blood bank, and the bedside of the patient is the main location.

Blood Banks↗
PubMed1980

The focus-to-detector distance as a source of systematical errors in the measurement of Chaoul therapy units.

The skin exposure rates measured on 22 Chaoul units in two consecutive years were compared and their variance was analysed. The statistical fluctuation of the ionization method was 3.1% by a factor of about 2 to 2.5 smaller than the variations due to lack of reproducibility of the Chaoul units. The authors observed systematical errors among exposure rate measurement performed at different focus-to-detector distances. The effective source-to-detector distance is different for various ionization chambers. It is the sum of nominal focus-to-detector distance plus a geometrical constant. The geometrical constant is for a particular chamber only to a small extent dependent on the front wall thickness and on the focus-to detector distance. Sufficient standardization of both calibration procedure and construction of ionization chambers may help in avoiding this effect.

Analysis of Variance↗
PubMed1985

Grading of tenderness as a source of interrater error in the Ritchie articular index.

To assess the effect of grading of tenderness on the interrater reliability of the Ritchie articular index (RAI), 3 physicians recorded independent joint scores on each of 18 patients, examined in random order. Our results indicate that close agreement (Intraclass Correlation Coefficient = 0.85) can be achieved on global RAI scores, and that raters can achieve reasonable agreement (kappa = 0.40-0.59) on the absolute presence or absence of tenderness of individual joints. By contrast, interrater agreement hardly exceeds the chance level (kappa = 0.008-0.148) when degree of tenderness is independently assessed. The grading system of the RAI may thus be implicated as an important source of the instrument's interrater error.

Adult↗
PubMed2003

Identifying sources of verification errors in progressive addition lenses.

BACKGROUND: Occasional disagreement over spectacle lens prescription accuracy between the optical laboratory and the practitioner is to be expected, especially with a progressive addition lens (PAL). The PAL continues to evolve in design, yet retains some unique, inherent problems. The purpose of this study was to determine if the source of these problems results from the lens design, laboratory error, or verification procedures. METHODS: Six Varilux Comfort Orma Supra progressive addition lenses were surfaced to plano distance power, and then verified using manual and automatic lensmeters. The same lenses were then re-surfaced for various sphere and cylinder powers, and verified in the same manner. The results of each trial were spherocylindrically averaged, and compared to the desired result. The lenses were also verified by several incorrect methods to investigate positional tolerance during verification and possible verification errors. RESULTS: The averages for the lenses surfaced to the "prescribed" power were not far from the expected power by all measurement techniques when measured at the central DRP location. Positional errors of as little as 2 mm from the DRP center, however, can lead to erroneous results. CONCLUSION: Unless correct verification procedures are carefully followed, progressive lenses can be mistakenly identified as being in error when they are not.

Eyeglasses↗
PubMedDate not supplied

An overview of errors in line source dosimetry for gamma-ray brachytherapy.

The generally used approach for routine brachytherapy dosimetry depends on a value of source strength provided by the source supplier, the theoretical concept of exposure rate constants for different nuclides, and the applicability of inverse square law to point sources. Corrections for filtration of the radiation within the capsule of the source and attenuation in tissue medium are effected based on attenuation coefficients and data published in the literature. Therefore there is no unique or ideal way of selecting the required data and there could be a spread in the dose values derived by different users. The errors inherent in the current practice of dosimetry of linear sources in brachytherapy are discussed. If the brachytherapy sources are specified in terms of exposure rate at a distance from the source by the source suppliers, the overall uncertainty in the dosimetry at regions of clinical interest around the source could be limited to about +/- 6%.

Brachytherapy↗
PubMed2004

Sources of systematic error in instruments measuring satisfaction with home care.

The concept of systematic error (SE) is used in this review as a framework for appraising the only two studies reporting psychometric testing of instruments of home-care satisfaction (HCS). The development of each tool is summarized. General sources of SE are discussed relative to instrumentation, the process of measurement, and participants. Sources of SE that researchers in HCS have tried to remedy in each category are covered. The typical approaches to those problems are critically analyzed relative to the validity of the construct of HCS. Ideas are proposed to enhance the empirical grounding of the construct through (a) eliciting and analyzing data about expectations as well as data about satisfaction and (b) counteracting the interaction among response set, direct referent items, and skewness in studies of HCS.

Bias↗
PubMed1994

A user's guide for avoiding errors in absorbance image cytometry: a review with original experimental observations.

The sources of errors which may occur when cytophotometric analysis is performed with video microscopy using a charged-coupled device (CCD) camera and image analysis are reviewed. The importance of these errors in practice has been tested, and ways of minimizing or avoiding them are described. Many of these sources of error are known from scanning and integrating cytophotometry; they include the use of white instead of monochromatic light, the distribution error, glare, diffraction, shading distortion, and inadequate depth of field. Sources of errors specifically linked with video microscopy or image analysis are highlighted as well; these errors include blooming, limited dynamic range of grey levels, non-linear responses of the camera, contrast transfer, photon noise, dark current, read-out noise, fixed scene noise and spatial calibration. Glare, contrast transfer, fixed scene noise, depth of field and spatial calibration seem to be the most serious sources of errors when measurements are not carried out correctly. We include a table summarizing all the errors discussed in this review and procedures for avoiding them. It can be concluded that if accurate calibration steps are performed and proper guidelines followed, image cytometry can be applied safely for quantifying amounts of chromophore per cell or per unit volume of tissue in sections, even when relatively simple and inexpensive instrumentation is being used.

Cytological Techniques↗
PubMed1997

Sources of diagnostic error in the fine-needle aspiration diagnosis of Warthin's tumor and clues to a correct diagnosis.

Squamous metaplasia and cystic degeneration in Warthin's tumor (WT) are not uncommon. A recent case of WT misdiagnosed as metastatic squamous carcinoma with cystic change prompted us to review our experience with fine-needle aspiration (FNA) of WT, with special attention given to potential sources of diagnostic pitfalls. Aspirations from 16 cases of histologically confirmed WT were retrospectively evaluated for cellularity, cell composition, and background. The FNA review diagnosis was compared with the previous FNA and corresponding tissue findings. All tumors presented in the parotid gland. The initial cytologic diagnoses were: WT in 13 cases, oncocytoma vs. low-grade mucoepidermoid carcinoma in 1, squamous carcinoma vs. branchial cleft cyst in 1, and squamous carcinoma in 1. On review, 13 cases (81%) showed typical features associated with WT: Moderate to abundant oncocytic epithelium, lymphoid stroma, background debris, and mild squamous metaplasia. In the remaining cases, one lacked a lymphoid stroma and could not be further classified (initially called "oncocytoma vs. low-grade mucoepidermoid carcinoma"). The other 2 cases contained moderate to abundant atypical squamous cells and extensive necrotic/mucoid debris, and review diagnoses were consistent with the initial cytologic diagnoses (squamous carcinoma in one, and branchial cleft cyst vs. squamous carcinoma in the other). In our series, typical features of WT were seen in 81% of cases. Atypical features are largely present as individual metaplastic squamous cells. Diagnostic errors are caused by a lack of typical features and the presence of individual atypical squamous cells in a necrotic background mimicking carcinoma. An awareness of the morphologic variation present on cytologic preparations and correlation with clinical findings should prevent erroneous interpretation in the FNA setting.

Adenolymphoma↗
PubMed2002

Accuracy of EEG source reconstruction in the presence of brain lesions: modelling errors and surface electrodes' placement.

Source localization techniques based on electroencephalography (EEG) use scalp potential data to infer the location of brain neural activity. A volume conductor model describing the electrical properties of the human head is needed. Lesions have conductivity considerably different from that of normal brain and should be included in the head model because the differences between the actual head and the model can cause source reconstruction errors. We performed a simulation study investigating EEG dipole source reconstruction errors, caused by brain lesions neglecting, using different measurement montages. The scalp was sampled by 64 electrodes (simulating clinical practice) and by 128 electrodes (extended configuration). The human head was represented by an eccentric-spheres model in which a modifiable eccentric bubble approximated various brain lesions. We analyzed 64 pathological situations. Results showed that neglecting brain lesions in source reconstruction procedures could cause large source localization errors which depended on source location and orientation, and varied with EEG montage. The maximum source localization errors (LE) were 2.5 cm and 1.4 cm for the 64 and 128 electrode configurations respectively. The largest errors occurred for sources nearby the lesion. LE was not systematically smaller with 128 rather than 64 electrodes. Maximum intensity errors were similar for 128 and 64 electrodes. The EEG inverse dipole solution was maximally sensitive to the electrode configuration on the scalp when the source was located deep in the brain (e.g. in the brain stem). We concluded that deep source localization needed an extended sampling of the scalp.

Brain Diseases↗