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At least 1,603 records · Page 89Linked to original sources
PubMed1988

Accuracy of pressure-flow estimates of velopharyngeal orifice size in an analog model and human subjects.

This study examined the accuracy of pressure-flow estimates of velopharyngeal (V-P) orifice size as applied to an analog model and two human subjects. Accuracy was assessed under differing conditions of degree of nasal resistance and type of instrumental interface. Known V-P orifice openings were introduced in the model through use of cover plates and in the humans through use of modified nasopharyngeal obturators. Nasal resistances were altered with perforated nasal plugs. Instrumental interfaces differed principally in the method used to detect nasal cavity pressure. Measures were applied to the hydrokinetic equation to estimate V-P area values. Data from the analog model and the human subjects were comparable in many respects. In low nasal resistance, area estimates were reasonably accurate regardless of the interface utilized. In high nasal resistance error typically increased, although not equally across interface types. Potential sources of error are identified and discussed.

Adult↗
PubMed2000

Limitations of long-path averaging instruments.

Long-path averaging instruments measure the average velocity or concentration of a substance or substances over an averaging path. These measurements are then often used for calculation of the average concentration and mass flow rate of the substance. The purpose of this paper is to describe some of the limitations of these instruments and to suggest ways in which these limitations can be minimized. Two limitations were examined: measuring concentration in a single dimension (e.g., ignoring the variation in concentration over the width of the sample plane), and deriving an average concentration without considering velocity effects. The resultant errors will be application-specific. Estimates of the second source of error can be obtained from the covariance of concentration and velocity profiles over the path length. Unfortunately, suitable field data were not available, and to illustrate the method, estimates of the error were obtained for a range of possible concentration and velocity profiles. Errors of 50% or greater in the mass flow were incurred for the concentration and velocity profiles considered. This error was reduced to a negligible level by segmenting the averaging path length. It is recommended that velocity and concentration profiles be obtained for a broad range of applications to enable the importance of covariance errors to be better assessed.

Air Pollution↗
PubMed2003

Semi-automated sensitivity analysis to assess systematic errors in observational data.

BACKGROUND: Published epidemiologic research usually provides a quantitative assessment of random error for effect estimates, but no quantitative assessment of systematic error. Sensitivity analysis can provide such an assessment. METHODS: We describe a method to reconstruct epidemiologic data, accounting for biases, and to display the results of repeated reconstructions as an assessment of error. We illustrate with a study of the effect of less-than-definitive therapy on breast cancer mortality. RESULTS: We developed SAS code to reconstruct the data that would have been observed had a set of systematic errors been absent, and to convey the results. After 4,000 reconstructions of the example data, we obtained a median estimate of relative hazard equal to 1.5 with a 95% simulation interval of 0.8-2.8. The relative hazard obtained by conventional analysis equaled 2.0, with a 95% confidence interval of 1.2-3.4. CONCLUSIONS: Our method of sensitivity analysis can be used to quantify the systematic error for an estimate of effect and to describe that error in figures, tables, or text. In the example, the sources of error biased the conventional relative hazard away from the null, and that error was not accurately communicated by the conventional confidence interval.

Bias↗
PubMed1988

Neoplasms of the central nervous system in Norway. I. Quality control of the registration in the Norwegian Cancer Registry.

The Norwegian Cancer registry includes reports on 8,933 cases of primary central nervous system neoplasms diagnosed in the period 1955-1984. Before submitting this data set to epidemiological analysis, errors were searched out and subsequently corrected, and a quality control was performed. First, seven categories of neoplasm records likely to be faulty were defined. In this way 109 cases (1.2% of the total) were identified for extensive study. Minor or major errors were found and corrected in 86 cases. The main source of error was misinterpretation of data by cancer registry staff (67 out of 109 cases). The second approach was to evaluate the quality of the corrected data set by a random draw of 300 cases. Errors concerning total incidence rates and rates for main groups of gliomas, meningiomas and neurilemmomas represented 0.3% of the total, and altogether 9.3% of errors of varying severity were revealed. The series is discussed with regard to prerequisites for serving as reliable data on CNS neoplasm epidemiology. The results indicate that the data from the Norwegian Cancer Registry is sufficiently valid for a thorough study of CNS neoplasms.

Brain Neoplasms↗
PubMed1986

Demographic event history analysis: a selective review.

This is a selective review of the literature concerning demographic event history analysis. "We have attempted to emphasize work that we consider to be particularly important or innovative, to note some of the difficulties that may arise with the use of event history analysis, and to point to several substantive areas where research is still poorly developed."

Data Collection↗
PubMedDate not supplied

Child survivorship estimation: methods and data analysis.

"The past 20 years have seen extensive elaboration, refinement, and application of the original Brass method for estimating infant and child mortality from child survivorship data. This experience has confirmed the overall usefulness of the methods beyond question, but it has also shown that...estimates must be analyzed in relation to other relevant information before useful conclusions about the level and trend of mortality can be drawn.... This article aims to illustrate the importance of data analysis through a series of examples, including data for the Eastern Malaysian state of Sarawak, Mexico, Thailand, and Indonesia. Specific maneuvers include plotting completed parity distributions and 'time-plotting' mean numbers of children ever born from successive censuses. A substantive conclusion of general interest is that data for older women are not so widely defective as generally supposed."

Americas↗
PubMed2002

Quantitative analysis of mannitol polymorphs. X-ray powder diffractometry--exploring preferred orientation effects.

Mannitol is a polymorphic parmaceutical excipient, which commonly exists in three forms: alpha, beta and delta. Each polymorph has a needle-like morphology, which can give preferred orientation effects when analysed by X-ray powder diffractometry (XRPD) thus providing difficulties for quantitative XRPD assessments. The occurrence of preferred orientation may be demonstrated by sample rotation and the consequent effects on X-ray data can be minimised by reducing the particle size. Using two particle size ranges (<125 and 125-500 microm), binary mixtures of beta and delta mannitol were prepared and the delta component was quantified. Samples were assayed in either a static or rotating sampling accessory. Rotation and reducing the particle size range to <125 microm halved the limits of detection and quantitation to 1 and 3.6%, respectively. Numerous potential sources of assay errors were investigated; sample packing and mixing errors contributed the greatest source of variation. However, the rotation of samples for both particle size ranges reduced the majority of assay errors examined. This study shows that coupling sample rotation with a particle size reduction minimises preferred orientation effects on assay accuracy, allowing discrimination of two very similar polymorphs at around the 1% level.

Excipients↗
PubMed1979

Biochemical changes in avian tissues during infection.

Major sources of error in studies of diet--infectious disease interactions relate to failure 1) to define the stage of a disease cycle; and 2) to determine the extent of disease involvement at time of sampling. The former can be determined from clinical and biochemical observations from time of inoculation to recovery or mortality; the latter can be calculated from indexes obtained from histological preparations, changes in body temperatures, and other clinical symptoms, including weight loss and efficiencies of feed utilization. Other significant errors are derived from the normal 24-hour dynamics of particular tissue constituents, which include oscillations and circadian rhythms. Experimental designs and accuracy of data are always helped by prior knowledge of 24-hour patterns of these normal fluctuations. For example, such patterns will reveal that enzyme and hormonal changes are far more dynamic than body water changes. Studies of nutrition--disease interactions are extremely complex and the researcher must be aware of and eliminate as many sources of experimental error as possible to avoid confounding the data.

Amino Acids↗
PubMed2005

Interfacing clinical practice and error prevention.

Medication error is a major source of preventable harm to patients in hospitals and is an area in which, it is suggested, information technology will have a positive impact. This paper presents findings from part of a study that examined current information utilisation patterns during nursing medication rounds. Nursing working patterns in medication administration are poorly understood despite being one of the most likely sources of medication error. Methods used were drawn from principles of Human Computer Interaction (HCI), using a semi-structured observational tool for analysing system requirements and data elements. Results from this study indicated that clinical and contextual factors impact on nursing patterns of information handling in many ways, including documentation quality, location of information sources and current patterns of computer utilization. Numerous extraneous interruptions also impact on the ability of nurses to assimilate and use clinical information effectively. These results were used to develop a conceptual framework for interfacing error prevention in clinical practice. These insights into the human factors that are the reality of clinical practice allow us to design and develop effective information technology systems to help prevent nursing medication administration errors.

Humans↗
PubMed1994

Bioengineering and the skin: from standard error to standard operating procedure.

Bioengineering techniques for examination of the skin, measuring principles and sources of error relative to technique, study design, measuring conditions and variability related to test subjects and preconditioning are reviewed. Principles of validation and standard operating procedures (SOP) are discussed, including guidelines for measurement of transepidermal water loss (TEWL) and laser Doppler cutaneous blood flow. Today typical errors are not related to a measuring device but to the way it is used.

Biomedical Engineering↗
PubMed1993

[Human errors in the calculation of the Monitor Unit in radiotherapy].

Human mistakes are a major source of error from the definition to the execution of a treatment planning. An unrevealed serious human error can cause therapy to fail therefore it is of fundamental importance to eliminate serious human errors during MU calculation. In this work the human error incidence in MU calculation is evaluated by an independent check. The investigation refers to 1,926 controls collected in about 18 months. Serious daily errors rate (errors causing a 5%, or higher, discrepancy on the daily reference dose) was 1.4% (27/1926). Serious global errors incidence (errors causing a 5%, or higher, discrepancy on the total reference dose) was 0.9% (15/1,731). The data show that the human error in MU calculation is not negligible; they also indicate the value of the independent control of MU, which is an important tool for quality assurance in radiotherapy (like in vivo dosimetry and portal imaging.

Bias↗
PubMed1982

Laboratory evaluation and assistance efforts: mailed, on-site and blind proficiency testing surveys conducted by the Centers for Disease Control.

During the last three years, the Centers for Disease Control (CDC) has conducted: 1) on-site surveys in which trained personnel visited laboratories that had experienced performance problems in the quarterly mailed proficiency testing (PT) program, reviewing the laboratories' analytical procedures by using carefully referenced samples to determine sources of errors and providing assistance in correcting them; 2) special assistance surveys in which carefully referenced samples were mailed to laboratories that had performed unsatisfactorily in routine mailed PT surveys and then telephone consultations were conducted to correct the problems; and 3) blind surveys in which carefully referenced samples were sent through normal patient sample acquisition routes to assess the actual day-to-day performance capability of the laboratories. Results suggest that on-site surveys by trained laboratory surveyors and special mailed assistance surveys can be very effective in identifying the source of analytical errors in laboratories previously found, through mailed PT surveys, to have performance problems. Blind-survey results indicate that good performance in mailed PT does not necessarily imply good laboratory performance with routine patient specimens. Although difficult to conduct, blind surveys should be conducted whenever the logistics can be worked out by contractors for laboratory services, clinicians using laboratory services, and the laboratories themselves to assure the continuation of quality service.

Blood Chemical Analysis↗
PubMed2004

Measuring the efficacy of insecticide treated bednets: the use of DNA fingerprinting to increase the accuracy of personal protection estimates in Tanzania.

Summary Insecticide-treated nets have proved successful in the prevention of malaria as a result of both the personal protection with which they provide the sleeper and also the 'mass effect' on the local mosquito population when they are used on a community-wide basis. Personal protection estimates are normally based on comparisons of the numbers of bloodfed mosquitoes found in rooms with and without nets, however it seemed possible that a number of those mosquitoes may not have fed on the occupants of the rooms in which they were found but had entered after feeding elsewhere. To address this possible source of error, we used an 8-locus microsatellite system to identify the source of bloodmeals of Anopheles gambiaes.l. and A. funestus mosquitoes collected in rooms and window traps in Tanzanian villages with and without nets treated with alphacypermethrin. DNA fingerprints were produced from blood samples taken from people who had slept in these rooms and were matched to fingerprints obtained from the mosquito bloodmeals. We were able to type successfully over 90% of the bloodmeals collected and found that proportions of bloodfed mosquitoes that had fed on occupants of the rooms in which they were found were high and only slightly greater in villages without treated nets than those with them (95% and 88%, respectively). When these percentages were used to adjust estimates of personal protection, it was found that the error due to mosquitoes not feeding in the rooms in which they were collected is negligible.

Adult↗
PubMed1984

Reproducibility of radiographs with the orthopantomograph 5: tooth-length assessment.

The precision of tooth-length assessments based on repeated panoramic radiographs made with a Siemens OP 5 was investigated in three groups of twenty patients. Two exposures of the same patient were made under three different radiographic conditions. Of the tooth lengths, nonmeasurability was found in 14% to 17%. The variability (standard deviation) of the measurements assessed from repeated radiographs ranged from 0.65 to 0.85 mm, or 2.4% to 3.1% of the mean radiographic tooth length in the different patient groups. The measurement error ranged from 0.43 to 0.56 mm, indicating that the main source of error inherent in the method was recognition of the reference points. Small differences were found between the tooth groups and between the right and left sides.

Adolescent↗