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At least 37 records · Page 2Linked to original sources
PubMed1991

[Sources of error in sonographic diagnosis of the rotator cuff].

Sonography of the shoulder joint has developed into an established examination technique in the diagnosis of periarticular lesions of the shoulder. Sonographic diagnosis of the rotator cuff in particular contains a multitude of possible errors, which are gone into by this study by means of 149 clinically, radiologically and sonographically examined shoulder patients with an average age of 50.5 years. Besides errors made by wrong examination technique such of the transducer as incorrect adjustment of the equipment, insufficient contact of the transducer with the skin and unsuitable choice of the examination plane, there are sources of errors in the interpretation of the sonogram caused by lack of knowledge about physically caused artifacts and sonoanatomical qualities of the shoulder joint. Calcification inside the rotator cuff and the so-called "sonographic inhomogeneity of the rotator cuff" are numbered among the sources of error particular to the shoulder joint. Most errors in sonographic diagnosis of the rotator cuff can be avoided by careful examination of both shoulder joints with an exactly tuned ultrasound device, taking into account the sonoanatomical and ultrasonic qualities. Radiological examination of the affected shoulder joint cannot be replaced by ultrasound.

Diagnostic Errors↗
PubMed1978

Potential source of error in official diazepam assays.

A possible source of interference by a benzophenone hydrolysis product with the USP XIX spectrophotometric determination of diazepam in dosages forms is reported. A minor adaptation of the official assay procedures is briefly proposed as one method to correct this error.

Diazepam↗
PubMed1979

Petri dish concavity--a potential source of error in antibiotic assay and agar diffusion antibiotic susceptibility tests.

Concave deformaties of the bottom of Petri dishes are a potential source of error for disk agar diffusion antibiotic assay and susceptibility procedures. This is due to differences in agar depth between the central and peripheral areas of the Petri dishes. We have observed significant concave deformities in both empty and commercially filled 150-mm plastic Petri dishes. For this reason we recommend that inspections for Petri dish deformity be incorporated into microbiology laboratory quality control programs.

Anti-Bacterial Agents↗
PubMed1976

Some sources of error and their effect on Census statistics.

Often the reliability of survey data is examined only in relationship to sampling variances, excluding many other potential sources of error. If the sampling variance dominates the mean-square error, then few mistakes result by considering sampling variance only; however, if sampling variance is only a small part of the mean-square error, serious mistakes in inference could be made. The Bureau of the Census has developed a model describing the joint effect of sampling and nonsampling errors on census statistics. This article shows how a study of the components of error may lead to methods of improving the accuracy and reliability of survey data.

Demography↗
PubMed1977

Sources of error in measuring cerebrospinal fluid formation by ventriculocisternal perfusion.

Ventriculocisternal perfusion is regarded as a precise method of measuring the rate of formation of cerebrospinal fluid (CSF) but it possesses inherent potential sources of error. Using the technique to measure CSF formation rate in the rhesus monkey, we have observed rate changes when none were expected. Most puzzling has been the steady decline of CSF formation rate at 4 percent each hour during the final five hours of a seven hour perfusion although variables known to affect CSF formation remained stable. In addition, alterations in rate caused by artefacts were observed in experiments in which craniospinal blood volume was changed by sudden changes of either PCO2 or central venous pressure. Mobilisation or sequestration of incompletely equilibrated CSF is believed responsible. In other experiments, a small increase of intracranial pressure produced by increasing outflow resistance was quickly followed by an apparent reduction of CSF formation. We have concluded that to assess accurately the effect a variable has on the rate of CSF formation, one must control perfusion time and craniospinal blood volume as well as intracranial pressure.

Animals↗
PubMed1991

Accuracy of end-tidal carbon dioxide tension analyzers.

Substantial mean differences between arterial carbon dioxide tension (PaCO2) and end-tidal carbon dioxide tension (PETCO2) in anesthesia and intensive care settings have been demonstrated by a number of investigators. We have explored the technical causes of error in the measurement of PETCO2 that could contribute to the observed differences. In a clinical setting, the measurement of PETCO2 is accomplished with one of three types of instruments, infrared analyzers, mass spectrometers, and Raman spectrometers, whose specified accuracies are typically +/- 2, +/- 1.5, and +/- 0.5 mm Hg, respectively. We examined potential errors in PETCO2 measurement with respect to the analyzer, sampling system, environment, and instrument. Various analyzer error sources were measured, including stability, warm-up time, interference from nitrous oxide and oxygen, pressure, noise, and response time. Other error sources, including calibration, resistance in the sample catheter, pressure changes, water vapor, liquid water, and end-tidal detection algorithms, were considered and are discussed. On the basis of our measurements and analysis, we estimate the magnitude of the major potential errors for an uncompensated infrared analyzer as: inaccuracy, 2 mm Hg; resolution, 0.5 mm Hg; noise, 2 mm Hg; instability (12 hours), 3 mm Hg; miscalibration, 1 mm Hg; selectivity (70% nitrous oxide), 6.5 mm Hg; selectivity (100% oxygen), -2.5 mm Hg; atmospheric pressure change, less than 1 mm Hg; airway pressure at 30 cm H2O, 2 mm Hg; positive end-expiratory pressure or continuous positive airway pressure at 20 cm H2O, 1.5 mm Hg; sampling system resistance, less than 1 mm Hg; and water vapor, 2.5 mm Hg. In addition to these errors, other systematic mistakes such as an inaccurate end-tidal detection algorithm, poor calibration technique, or liquid water contamination can lead to gross inaccuracies. In a clinical setting, unless the user is confident that all of the technical error sources have been eliminated and the physiologic factors are known, depending on PETCO2 to determine PaCO2 is not advised.

Algorithms↗
PubMedDate not supplied

Factors influencing the accuracy of the cardiac output monitoring and diagnostic unit for pneumatic artificial hearts.

The Cardiac Output Monitor and Diagnostic Unit (COMDU) has been the most widely used method to noninvasively determine cardiac output in pneumatic ventricles for the past 10 years. Clinical observation has suggested a discrepancy between the COMDU and expected cardiac outputs. In vivo tests verified and quantified this error. The error sources were examined using in vitro test conditions, with both the inflow and outflow, as well as COMDU flow readings, being analyzed. Transducer and calibration error sources were also identified, and the accuracy of the method for determining cardiac output for the in vitro test conditions was quantified. With a more accurate calibration scheme, the in vitro average error was reduced from -16.2% (range of 0.1% to -41.1%) to 0.1% (range 4.8% to -3.65). The major error sources were identified as missed inflow, transducer calibration and drift, and system variance.

Animals↗
PubMed1989

Interactions with hemoglobin: a source of error in measurements of transketolase activity in hemolysates.

Measurements of the activity of transketolase in human erythrocyte lysates by an assay coupled to NADH oxidation indicate that interactions of assay substrates with hemoglobin can give rise to overestimations of transketolase activity. Three potential sources of error are identified. Thus, in lysates containing methemoglobin, NADH oxidation can be due firstly to methemoglobin reductase activity or secondly to the monooxygenase activity of methemoglobin, for which the substrate can be ribose 5-phosphate, a substrate also of transketolase. Thirdly, the addition of high concentrations of the transketolase cofactor, TDP, to an insufficiently buffered reaction mixture can cause the aggregation and precipitation of hemoglobin: a phenomenon that may be misconstrued as an enhanced increase in absorbance at 340 nm and hence as additional transketolase activity. Although the present study concentrates on these potential artefacts in assays of transketolase activity, the findings may well be relevant to the measurement of other enzyme activities in hemolysates by procedures based ultimately on the rate of consumption or production of NAD(P)H.

Chromatography, Gel↗
PubMedDate not supplied

Measurement of blood flow by ultrasound: accuracy and sources of error.

Doppler ultrasound has now developed to the point where the rate of flow of blood in a given vessel can be measured with appropriate instrumentation. The theoretical basis of Doppler flow measurement is reviewed in this paper, with particular emphasis on the potential and actual sources of error. Three distinct approaches are identified, and the strengths and weaknesses of each discussed. The separate errors involved in estimating the vessel cross-sectional area, the angle of approach, and the Doppler shift are analyzed, together with the question of the uniformity of scattering from the blood. In vivo and in vitro tests of the accuracy obtained using a number of Doppler flow measuring instruments are then reviewed. It is concluded that the Doppler methods are capable of good absolute accuracy when suitably designed equipment is used in appropriate situations, with systematic errors of 6% of less. There are, however, considerable random errors, attributable primarily to errors in measuring the cross-sectional area and the angle of approach. Repeating the measurement of flow several times and averaging the results can reduce these random errors to an acceptable level.

Blood Flow Velocity↗
PubMed1975

Tissue sampling as a potential source of error in experimental studies of cartilage.

Although it might seem trite to point out that tissue sampling is a potential source of experimental error, this survey disclosed that even experienced investigators in fact often work with cartilage that is contaminated by non-cartilaginous tissue of which they were unaware. Twenty-two specimens ranging from chick embryo sternum to bovine nasal septum were studied by serial sectioning. Eighteen of the 22 contained extraneous tissue comprising from 3 to 50% of the cross-sectional area. The impact of the contamination depends on the use being made of the material and probably is greatest in cell culture studies because chondrocytes and fibroblasts have large differences in population doubling time. Several approaches for minimizing the error are suggested by the findings. Histological examination of specimen material is thus a desirable quality control procedure in the design and interpretation of experiments on cartilage as well as other tissues.

Animals↗
PubMed1975

[Sources of error in the radioimmunochemical determination of digoxin in serum].

In a study with numerous samples of serum we compared 5 Digoxin RIA and evaluated the reliability of tests by simultaneous determinations. There were found considerable differences in the determinations with the various RIA for the same serum; evident differences also were recorded in the recovery and in the reproducibility of the assays. Among some other sources of error the dependence of temperature and of the duration of the dextran-charcoal separation were observed; therefore, the charcoal incubation is recommendable at 4 degrees C. Each laboratory which is able to perform the determinations of digoxin concentrations in the serum should declare its own range for the therapeutic and toxic levels for the used RIA in collaboration with the clinicians.

Absorption↗
PubMed1987

[Sonographic diagnosis of hip dysplasia. Principles, sources of error and consequences].

Sonography of the hip in infants is being increasingly employed. This method of examination involves several specialist disciplines. The more widespread its use, the greater the likelihood of faulty diagnoses if one is not aware of its weak points. Faulty diagnoses are the order of the day if the method is employed by persons whose knowledge has not been updated to latest advances in the field; other sources of error are faulty scanning, unsuitable sonographic equipment and insufficient documentation. Hence, it is mandatory to describe the demands to be made on the equipment according to update standards and to draw up guidelines that will help to avoid quality loss. The criteria for assessing a hip sonogram are defined and the problem of age limit is considered. A review is given of disturbances of normal development of the hip. The possibility of effecting dynamic examination should not mislead one to neglect assessment of the hip joints as precisely as possible by means of an exacting measurement technique. The weak points of the technique of measurement and the valuation of the angles must be known. A review of the literature reveals many problems in hip sonography. A multitude of these problems is unnecessary and can be considered as solved if one would try to match modern quality demands and not be satisfied with a quality standard that is many years old. To achieve best possible hip examination via sonography it will often be necessary to considerably modify principles of general sonography of the soft parts.

Diagnostic Errors↗
PubMed1977

[The reaction time as a source of error in threshold audiometry (author's transl)].

An investigation of reaction times at the threshold of hearing is described. 96 subjects were classified into two groups of sensorineural hearing loss utilizing Types I and II Bekesy audiometry, and compared with one normal group as control. The results show that reaction times are largely unaffected by the type of hearing loss and test frequency. Increasing age, however, may result in increasing reaction times. These results and possible sources of error are discussed as effecting an exact threshold audiometry.

Adult↗
PubMedDate not supplied

[The reliability and sources of error in basic clinical documentation--a critical report of experiences].

Since 1. 1. 1985, computer-aided basic medical documentation has been routine at the University Orthopedic Clinic in Friedrichsheim, near Frankfurt. In addition to data on patient's histories, all data needed to satisfy the criteria of the Federal Directive on Operating Cost Rates are gathered. The diagnoses are stored in clear text, in a modified Eichler code, and according to ICD 9. Conversion from the Eichler code to ICD 9 is almost fully automated. In a study covering 100 hospitalized cases the following findings were obtained relating to sources of error and reliability: Without any additional in-house plausibility checks, the rate of error in the ID code, created by coding family name, date of birth, and sex, was 7%. In clear text all diagnoses except one and all forms of therapy were correctly reproduced as contained in the medical report. On the other hand, 7% of the conversions into the Eichler code contained errors. The reason for the difference in the quality of data is pointed out. In some of the other surveys, e.g., of infection rates, the rates of error were very high; most errors had been caused by the ward physicians. Data quality is enhanced by exploitation of routine process data when these control administrative procedures or are used for communication between physicians, since they then become relevant to actions and decisions and hence have to be reliable, regardless of documentation purposes.

Bone Diseases↗
PubMed1986

Heterophilic antibody as a source of error in immunoassay.

We describe our experience with a young woman believed to be hypothyroid and menopausal because of erroneously elevated TSH, LH, and FSH estimates. These errors were found to be due to the presence of antibodies to rabbit IgG in the patient's blood. We found that antibody-limited assays for TSH, LH, and FSH using antisera raised in rabbits were affected by this problem unless rabbit IgG was included, whereas antibody-excess assays were not. These problems were most simply detected by observing inappropriate results when measurements were made in dilutions of the patient's serum. The presence of endogenous antibody directed against antibodies used in immunoassays is a significant potential source of error requiring awareness on the part of both the clinician caring for such patients and the clinical laboratory making the measurements.

Adult↗
PubMed1976

Bubbles in samples for blood gas determinations. A potential source of error.

The presence of small gas bubbles in devices used to collect blood gas samples is considered. A gas bubble whose relative volume is 0.5 to 1% or more that of the liquid in the collection device is a potential source of significant error. Relationships describing the possible magnitude of this error are derived and substantiated.

Blood↗
PubMed1987

Sources of error and variability in the determination of anaerobic threshold in healthy humans.

The derivation of anaerobic threshold (AT) from the ventilatory responses to incremental exercise is associated with several sources of variability including true biological variability and the error attributable to the observer interpretation of data. To define and quantitate the sources of variability in AT determination we exercised 6 healthy volunteers 6 times and submitted plots of ventilation (Ve), CO2 production (VCO2), respiratory exchange ratio (R) and the ventilatory equivalent for oxygen (Ve/VO2) in random order to 4 independent observers. Within-subject variability in AT ranged from 7 to 55% depending on the subject, ventilatory parameter and observer with an overall mean coefficient of variability of 24%. Significant day-to-day variability was demonstrated in 4 of the 6 subjects using AT values derived from at least one of the ventilatory parameters (Anova, p less than 0.05-p less than 0.001). Mean values for AT obtained with the Ve and VCO2 plots (1.91 and 1.69 liter/min VO2) were significantly lower than those obtained from R and Ve/VO2 plots (2.28 and 2.6 liters/min VO2; p less than 0.001, Anova). Anova showed significant differences in AT values derived by one of the observers compared to the other three (p less than 0.001). A significant observer/ventilation parameter interaction was also found (p less than 0.001) due to one observer consistently estimating higher values of AT from the R plots. The observer error in deriving AT from each exercise test using the Ve plots = 24%, for VCO2 = 19% for R = 29% and for Ve/VO2 = 15%.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗