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PubMed1985

The limitations of atmospheric dispersion data and their contribution to uncertainties in dose assessment.

The calculation of atmospheric dispersion patterns is often an important component of radiation dose estimates. These dispersion calculations are a possible source of error and such errors or uncertainties need to be quantified. An important source of uncertainty is the meteorological data used in the calculations. Such data may be less than ideal because of constraints imposed by both availability and by the variances associated with population from which the data are obtained. We have studied a simple and much used model of atmospheric dispersion--the Gaussian plume. We discuss the uncertainties on the meteorological data which are input to the model and how these uncertainties could be used to estimate uncertainties for the modeling results. In doing this we have addressed both the uncertainty associated with a recorded climatology and the added uncertainty arising from the year-to-year variability at any given location.

Air Pollution, Radioactive↗
PubMedDate not supplied

Symptom perception and evaluation in childhood asthma.

BACKGROUND: Inaccuracies in symptom perception may contribute to morbidity and mortality in childhood asthma. OBJECTIVE: To systematically examine the accuracy of symptom perception on the part of children with asthma and their parents, as well as their interpretation and evaluation of the symptoms. METHOD: Twenty-eight patient/parent pairs from suburban and underserved urban pediatric populations participated in a 5-week protocol tracking subjective assessments of asthma severity (visual analog scales) and peak expiratory flow rates. Relationships between perceptual accuracy and demographic and disease factors were investigated. RESULTS: Adolescents were more accurate than school-aged children, more accurate children had better morbidity outcomes, and African American parents were more accurate than Caucasian parents. Socioeconomic status did not affect accuracy. Both children and parents missed early symptoms and waited too long prior to intervening in an exacerbation. CONCLUSIONS: There are multiple opportunities for error in symptom perception and evaluation. Identification of the source of error is critical to the effective utilization of education on self-management.

Adolescent↗
PubMed1986

Oxygen analyzers in anaesthesia: performance in a simulated clinical environment.

Nine commercial oxygen analyzers were tested in a laboratory model stimulating clinical anaesthesia conditions. Fifteen test situations were used in order to study the effects of nitrous oxide, humidity, positive end-expiratory pressure, halothane, enflurane and isoflurane. Errors exceeding 8 vol% were not uncommon, the dominating source of error being humidity. Analyzers with efficient dehumidification of gases before analysis performed better than analyzers without this property.

Anesthesiology↗
PubMed2006

Medication errors with the use of allopurinol and colchicine: a retrospective study of a national, anonymous Internet-accessible error reporting system.

OBJECTIVE: To more closely assess medication errors in gout care, we examined data from a national, Internet-accessible error reporting program over a 5-year reporting period. METHODS: We examined data from the MEDMARX database, covering the period from January 1, 1999 through December 31, 2003. For allopurinol and colchicine, we examined error severity, source, type, contributing factors, and healthcare personnel involved in errors, and we detailed errors resulting in patient harm. Causes of error and the frequency of other error characteristics were compared for gout medications versus other musculoskeletal treatments using the chi-square statistic. RESULTS: Gout medication errors occurred in 39% (n = 273) of facilities participating in the MEDMARX program. Reported errors were predominantly from the inpatient hospital setting and related to the use of allopurinol (n = 524), followed by colchicine (n = 315), probenecid (n = 50), and sulfinpyrazone (n = 2). Compared to errors involving other musculoskeletal treatments, allopurinol and colchicine errors were more often ascribed to problems with physician prescribing (7% for other therapies versus 23-39% for allopurinol and colchicine, p < 0.0001) and less often due to problems with drug administration or nursing error (50% vs 23-27%, p < 0.0001). CONCLUSION: Our results suggest that inappropriate prescribing practices are characteristic of errors occurring with the use of allopurinol and colchicine. Physician prescribing practices are a potential target for quality improvement interventions in gout care.

Adverse Drug Reaction Reporting Systems↗
PubMed1998

A comparison of manual versus computer-assisted radiographic measurement. Intraobserver measurement variability for Cobb angles.

STUDY DESIGN: A comparison between computer-assisted measurement using digitized radiographs, which has the potential to reduce error, and manual measurement using standard radiographs. OBJECTIVE: To assess measurement variability for the Cobb method on digital radiographs and compare it with that of manual measurements on standard radiographs. BACKGROUND DATA: Studies of the Cobb method have demonstrated multiple sources of error leading to significant intraobserver measurement variability. Estimates for the 95% confidence interval for intraobserver variability range from 2.8 degrees to 10 degrees. METHODS: Twenty-four scoliosis radiographs were measured by six examiners. Two measurement sets were done manually ("manual set"), and two measurement sets were done on digitized images using a computer mouse ("computer set"). RESULTS: For the manual set, the 95% confidence interval for intraobserver variability was 3.3 degrees (range, 2.5-4.5 degrees). For the computer set, the value was 2.6 degrees (range, 2.3-3.3 degrees). This difference in 95% confidence intervals between the manual and computer sets was statistically significant (P < 0.001). CONCLUSIONS: The results of this study demonstrate that intraobserver variability for manual and computer Cobb angle measurements yield a 95% confidence interval of approximately 3 degrees, with the computer having a slightly lower variability. The computer technique removes sources of intrinsic error, e.g., the variability introduced by using different manual protractors, the inaccuracy of standard protractors, and the use of wide-diameter radiographic markers. Identical digital images can be shared electronically between centers, without having to duplicate and mail films. Multicenter studies in which different examiners will be measuring Cobb angles may consider using the computer as a measuring device to reduce intrinsic measurement errors.

Arthrography↗
PubMed1999

Potential errors in FTIR measurement of oxidation in ultrahigh molecular weight polyethylene implants.

Potential sources of error in the use of FTIR to measure the level of oxidation in ultrahigh molecular weight polyethylene acetabular cups were evaluated using cups from a hip simulator wear study with and without artificial aging, as well as cups retrieved from clinically failed hip prostheses. Oxidation was measured as a function of depth below the bearing surface using transmission FTIR on microtomed sections of the cups. To account for the variation of the thickness of the microtomed sections, oxidation was plotted as the ratio of the absorbance of the carbonyl groups to the absorbance of a reference band at 2022 cm-1. Overnight soaking in hexane reduced the apparent levels of oxidation, presumably due to the extraction of absorbed contaminants. In cups with low to moderate levels of oxidation, the reference absorption was relatively independent of the level of oxidation and was linearly proportional to the thickness of the specimens, providing reproducible oxidation ratios. However, the scatter in the reference absorption and in the apparent oxidation ratio increased with increasing levels of oxidation and was greatest for the thickest (400 microm) microtomed sections. The profiles of the oxidation ratios for a given specimen that were plotted by the present study method could be numerically adjusted to coincide with the ratios plotted using the methods of two previous investigators, providing conversion factors that are useful for comparing results among the studies.

Animals↗
PubMed2004

Issues in association analysis: error control in case-control association studies for disease gene discovery.

Several sources of errors are discussed. While genotyping errors have little effect on power in case-control association studies, they tend to strongly increase false positive results in TDT type tests unless occurrence of errors is allowed for in the analysis (e.g., TDTae test). Disregarding non-genetic risk factors is shown to lead to a form of hidden heterogeneity, which can strongly reduce power. Stratification of data into more homogeneous subgroups is advocated as a simple solution to allowing for non-genetic risk factors such as socio-economic status and food preferences.

Case-Control Studies↗
PubMed1997

Computerized method of lesion volume quantitation in multiple sclerosis: error of serial studies.

This study was designed to evaluate a potentially important source of error in T2-hyperintense lesion measurement unique to longitudinal multiple sclerosis treatment trials that would not be detected by the standard intraobserver and interobserver error analyses. The effect of this "error of serial studies" was tested by using the standard-of-reference manual-outlining approach and a modified bi-feature space (statistical) approach applied to a database of five consecutive patients. To simulate the conditions of a longitudinal treatment trial, each patient had immediate repeat MR studies of the brain with imperfect head repositioning. The study hypothesis was confirmed that with an improved quantitative methodology, the "error of serial studies" (interseries error) would exceed the intraobserver error.

Brain↗
PubMed2006

Assessment of imaging studies used with radiosurgery: a volumetric algorithm and an estimation of its error. Technical note.

The Gamma Knife has played an increasingly important role in the neurosurgical treatment of patients. Intracranial lesions are not removed by radiosurgery. Rather, the goal of treatment is to induce tumor control. During planning, the creation of dose-volume histograms requires an accurate volumetric analysis of intracranial lesions selected for radiosurgery. In addition, an accurate follow-up imaging analysis of tumor volume is essential for assessing the results of radiosurgery. Nevertheless, sources of volumetric error and their expected magnitudes must be properly understood so that the operator may correctly interpret apparent changes in tumor volume. In this paper, the authors examine the often-neglected contributions of imaging geometry (principally image slice thickness and separation) to overall volumetric error. One of the fundamental sources of volumetric error is that resulting from the geometry of the acquisition protocol. The authors consider the image sampling geometry of tomographic modalities and its contribution to volumetric error through a simulation framework in which a synthetic digital tumor is taken as the primary model. Because the exact volume of the digital phantom can be computed, the volume estimates derived from tomographic "slicing" can be directly compared precisely and independently from other error sources. In addition to providing empirical bounds on volumetric error, this approach provides a tool for guiding the specification of imaging protocols when a specific volumetric accuracy, or volume change sensitivity, for particular structures is sought a priori. Using computational geometry techniques, the volumetric error associated with image acquisition geometry was shown to be dependent on the number of slices through the region of interest (ROI) and the lesion volume. With a minimum of five slices through the ROI, the volume of a compact lesion could be calculated accurately with less than 10% error, which was the predetermined goal for the purposes of computing accurate dose-volume histograms and determining follow-up changes in tumor volume. Accurate dose-volume histograms can be generated and follow-up volumetric assessments performed, assuming accurate lesion delineation, when the object is visualized on at least five axial slices. Volumetric analysis based on fewer than five slices yields unacceptably larger errors (that is, > 10%). These volumetric findings are particularly relevant for radiosurgical treatment planning and follow-up analysis. Through the application of this volumetric methodology and a greater understanding of the error associated with it, neurosurgeons can better perform radiosurgery and assess its outcome.

Algorithms↗
PubMed2000

Culture, ritual, and errors of repudiation: some implications for the assessment of alternative medical traditions.

In this article, sources of error that are likely involved when alternative medical traditions are assessed from the standpoint of orthodox biomedicine are discussed. These sources include (1) biomedicine's implicit reductive materialism (manifested in its negative orientation toward placebo effects), (2) a related bias against ritual, and (3) cultural barriers to the construction of externally valid protocols. To overcome these biases, investigators must attend to ritualistic elements in alternative treatments and should recruit patients from appropriate cultural groups. Collaborative research may be the key. Benefits of collaborative research include (1) increased mutual respect and integration between culturally distinct groups and practices, (2) increased understanding and use of sophisticated techniques of empirical analysis among practitioners from the alternative traditions, (3) increased appropriation of the therapeutic benefits of ritual, and (4) enhanced overall benefit for patients of all cultural backgrounds.

Complementary Therapies↗
PubMed1999

The open circuit nitrogen washout technique for measuring the lung volume in infants: methodological aspects.

BACKGROUND: Lung volume measurement by nitrogen washout is widely used in infants, though a lack of accuracy and changes of calibration over time have been reported. The potential sources of error were explored in order to increase the accuracy and reliability of the technique. METHODS: A commercial system for nitrogen washout and a 0.5 litre calibrating syringe as a lung model were used to perform over 2000 in vitro washouts, including simulated rapid breathing, shallow breathing, periodic breathing, sighs, and brief apnoeas. A constant 10 l/min bias flow of oxygen and extended equipment warming times were employed. A collapsible breathing bag was incorporated into the washout circuit. Following a single two point calibration, known air volumes from 42 ml to 492 ml were measured by nitrogen washout over a 14 hour period. The flow waveform in the nitrogen mixing chamber during a washout in vitro, with and without the breathing bag in the circuit, was also studied. RESULTS: The mean coefficient of variation of all volumes was 0.66%. The mean difference between measured and known volumes was 0.30 ml (95% confidence interval (CI) -0.18 to 0.79). This difference was not statistically significant (p = 0.22). The mean percentage error was -0.1% (range -0.47% to 0.46%). Nitrogen calibration remained stable for 14 hours. Without the breathing bag flow transients were frequent in the mixing chamber during in vitro washout. CONCLUSIONS: This technique increases the accuracy in vitro and the precision in vivo of volume measurement by nitrogen washout. Sources of potential errors including baseline drifting and inadequate equipment warming times were identified. The breathing bag acted as a buffer reservoir, preventing large swings in flows within the nitrogen mixing chamber during washouts, and should be an integral component of the nitrogen washout circuit.

Breath Tests↗
PubMed1976

Definitions, sources and detection of laboratory error: a review.

Laboratory error has been estimated to occur in one to three percent of test results. Previous studies have identified common sources of laboratory-induced error. Methods of quality assurance are suggested to identify such errors and reduce the possibility of their reaching the physician. Present systems for monitoring quality assurance do not adequately detect biological and pharmacological errors.

Clinical Laboratory Techniques↗
PubMed2003

The study of some possible measurement errors in clinical blood electrolyte potentiometric (ISE) analysers.

The understanding of the most important sources of error in potentiometric blood analyser which might contribute to better instruments measurement repeatability is very often marginalized in fabrications and daily operation of some commercial blood analysers. In this paper ISEs-potentiometric measurements were performed and validated in Clinical Institute of Laboratory Diagnosis of the Zagreb University School of Medicine and Clinical Hospital Centre, using a carefully designed and constructed fully automated (computerised) homemade ISE-based blood electrolyte analyser constructed with an in-line five-channel flow-through measuring cell. The influence of electrolyte concentration of the salt bridge is reported. Special attention has been paid to the reference electrode design, and constructions which can operate in open liquid junction and membrane restricted liquid junction modes are described.

Calcium↗
PubMed1998

Improved distance analysis in RNA using network-editing techniques for overcoming errors due to spin diffusion.

Multispin magnetization transfer, or spin diffusion, is a significant source of error in NOESY-derived distance measurements for the determination of nucleic acid solution structures. The BD-NOESY and CBD-NOESY experiments, which allow the measurement of interproton distances with greatly reduced contributions from spin diffusion, have been adapted to structural analysis in RNA oligonucleotides. The techniques are applied to a lead-dependent ribozyme (LZ2). We demonstrate the measurement of both aromatic proton-aromatic proton NOEs free of spin diffusion involving the intervening ribose moieties and aromatic proton-ribose proton NOEs free of the efficient cross-relaxation within the ribose ring. In LZ2, the accuracy and precision of the resulting distances are significantly improved. We also find that, by allowing the use of longer mixing times with greater sensitivity, the experimental attenuation of spin diffusion in RNA increases the distance range of interactions that can be analyzed. This effect permits measurement of important long-range distances in LZ2 that are not accessible with standard techniques. Thus, these techniques allow the simultaneous optimization of the number, accuracy, and precision of distance constraints used for RNA structure determinations.

Base Sequence↗
PubMed2004

Infrared thermographic SAR measurements of interstitial hyperthermia applicators: errors due to thermal conduction and convection.

Thermal conduction and convection were examined as sources of error in thermographically measured SAR patterns of an interstitial microwave hyperthermia applicator. Measurements were performed in a layered block of muscle-equivalent phantom material using an infrared thermographic technique with varying heating duration. There was a 52.7% reduction in maximum SAR and 75.5% increase in 50% iso-SAR contour area for a 60-s heating duration relative to a 10-s heating duration. A finite element model of heat transfer in an homogeneous medium was used to model conductive and convective heat transfer during the thermographic measurement. Thermal conduction artefacts were found to significantly distort thermographically measured SAR patterns. Convective cooling, which occurs when phantom layers are exposed for thermal image acquisition, was found to significantly affect the magnitude, but not the spatial distribution, of thermographically measured SAR patterns. Results from this investigation suggest that the thermal diffusion artefacts can be minimized if the duration of the applied power pulse is restricted to 10 s or less.

Hot Temperature↗
PubMed2004

Alternative control volume geometries for measuring regurgitant flow through a valve.

Control-volume (CV) methods applied to magnetic resonance velocity-encoded cine images of the convergent proximal flow field of a regurgitant valve have been shown to measure reverse blood flow volume accurately. Spatial and temporal averaging are known to affect accuracy, but the effects of slice thickness and orientation relative to the flow field have not been systematically studied, nor have CV configurations requiring fewer scans been explored. Further, surface area calculations at the intersection of CV walls are a previously unrecognized source of error. Using a computational fluid dynamics model of steady flow through an orifice, we evaluated five different CV configurations in terms of accuracy, time costs, and clinical potential. CVs incorporating a basal wall were affected by blurring of axial velocity gradients near the orifice, and voxel grid alignment relative to the orifice was the most significant source of inaccuracy. Errors in surface area calculations at plane intersections produced deviations of 7-20%, depending on configuration. A CV formed by slices parallel to the orifice plane was deemed clinically unusable, while a cylindrical CV yielded good accuracy in simulated tests and showed potential for practical implementation based on scan time, ease of view selection, and visualization of the flow field.

Blood Flow Velocity↗
PubMed2006

Geocoding in cancer research: a review.

There is now widespread agreement that geographic identifiers (geocodes) should be assigned to cancer records, but little agreement on their form and how they should be assigned, reported, and used. This paper reviews geocoding practice in relation to major purposes and discusses methods to improve the accuracy of geocoded cancer data. Differences in geocoding methods and materials introduce errors of commission and omission into geocoded data. A common source of error comes from the practice of using digital boundary files of dubious quality to place addresses into areas of interest. Geocoded data are linked to demographic, environmental, and health services data, and each data type has unique accuracy considerations. In health services applications, the accuracy of distances computed from geocodes can differ markedly. Privacy and confidentiality issues are important in the use and release of geocoded cancer data. When masking methods are used for disclosure limitation purposes, statistical methods must be adjusted for the locational uncertainty of geocoded data. We conclude that selection of one particular type of geographic area as the geocode may unnecessarily constrain future work. Therefore, the longitude and latitude of each case is the superior basic geocode; all other geocodes of interest can be constructed from this basic identifier.

Biomedical Research↗
PubMed2002

Analysis and quantification of prescribing and transcription errors in a paediatric oncology service.

OBJECTIVE: To analyse and quantify the omission errors linked to physicians' prescribing and errors linked to nurses' transcription and to identify the type and frequency of factors associated. No pharmacological factors are taken into account. DESIGN: Analysis of physicians' prescriptions and nurses' transcriptions in chemotherapeutic treatments (20 patient files) and non-chemotherapeutic treatments (20 patient files); retrospective study. SETTING: Paediatric onco-haematology unit. MAIN OUTCOME MEASURES: Categorisation of physicians' prescriptions as complete or incomplete, categorisation of the various nurses' transcriptions as correct or incorrect. RESULTS: Physicians' prescriptions were complete for 61.6% of non-chemotherapy treatments. As each prescription is transcribed twice, two nurses' transcription sheets are filled in by the nurses. At the first transcription 79.3% of non-chemotherapy prescriptions and 88.2% of chemotherapy prescriptions were transcribed correctly, while in the second sheet these percentages were respectively 96.2% and 93.7%. CONCLUSIONS: Too many sheets of paper generate confusion and increase the risk of errors. The several transcriptions are, in both types of treatment, sources of errors. The problems identified in this study allowed us to open a discussion as how to improve the physicians prescriptions and the nurses' transcription sheets.

Child↗