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At least 109 records · Page 6Linked to original sources
PubMed1980

Possible sources of error in the evaluation of psychopathology.

Mental health professionals have been described as biased in the evaluation of mental illness, almost always in favor of illness. It is a professional bias does exist, two factors could be responsible--situational expectancies and/or professional training. Undergraduate students (N = 32) and psychiatric residents (N = 16) listened to four recorded interviews. Two levels of mental illness expectany were obtained by changing the context of the interviews. The Ss rated the interviewees on scales of psychopathology and recorded their impression of the interviewees. Multivariate and univariate analysis of variance and chi 2 tests were used to evaluate the data. Evidence indicated that the biased perception of mental illness occurred for all Ss when mental illness expectancies were high. The data also indicated that residents are not more inclined than students to label people mentally ill.

Attitude of Health Personnel↗
PubMed1989

Measurement of coronary sinus flow by thermodilution: observations on the effect of respiration and a review of the potential sources of error.

In a series of experiments involving measurement of left ventricular blood flow by thermodilution in the coronary sinus, a consistent, but unexpected, variation in calculated coronary sinus flow, related to respiration, was seen. In some patients the variation was small, but in others it was as much as 300%. To discover its cause, five patients were investigated prospectively with continuous right atrial pressure monitoring during coronary flow measurement and respiratory manoeuvres. In three, ice-cold saline was injected into the right atrium during respiratory manoeuvres while coronary sinus temperature was monitored continuously and the position of the catheter was monitored fluoroscopically. The cause was found to be movement of the catheter such that thermistor approached the right atrium, and the variation was therefore spurious. We report these findings and discuss other known causes of inaccurate coronary flow measurement using the thermodilution technique.

Blood Flow Velocity↗
PubMed1993

Sources of error in quantitative coronary angiography.

Many studies have reported the accuracy of quantitative coronary angiography (QCA) based on experiments using moderated-size phantoms imaged under unrealistic radiographic conditions. However, these observations may not be generalizable to the setting of clinical angiography. To determine QCA accuracy in a realistic radiographic setting and evaluate the impact of the x-ray system line spread function, plexiglass phantoms were imaged inside and out of a human thorax. A realistic radiographic background was associated with a 38% increase in variability of results (p < 0.05). Low concentrations of contrast and large image intensifier input screens were associated with significantly larger errors and variability in results (p < 0.05). There was a systematic overestimation of diameter in the smallest phantom. A mathematical model of the x-ray line spread function was developed that explains the observed overestimation of the smallest phantom and provide a rational approach for correction of the line spread function for QCA. Many factors encountered in clinical coronary angiography such as nonuniform radiographic background, low concentrations of contrast, and small vessel diameters have a significant adverse impact on the accuracy and/or variability of gradient-based edge detection QCA systems.

Artifacts↗
PubMed1983

Accuracy of various techniques in the measurement of the duration of the Q wave: a possible source of error in diagnosing myocardial infarction by electrocardiography.

The method of measuring the width of the Q wave on electrocardiogram is one of the variables contributing to conflicting findings regarding the accuracy of the ECG in the diagnosis of myocardial infarction. This study assesses the accuracy of a variety of methods of measuring the width of the Q wave recorded by direct-writing electrocardiographic instruments. The assessment was made by comparing the width of the Q wave as inscribed by thermal direct-writing electrocardiographs to the width of the Q wave as measured from an oscilloscopic display, the latter representing the "true" width of the Q wave. The measurement of the width as obtained from the upper edge of the tracing obtained with direct-writing electrocardiographs underestimated the true width of the Q wave, while the opposite was the case by measuring the width along the lower edge of the tracing. The most reliable ways to obtain the true width of the Q wave are: (1) to average the measurements as obtained along the upper and lower edge, (2) to measure the width along an ideal line in the middle of the tracing, or (3) to measure the width along the trailing edge of the deflection.

Diagnostic Errors↗
PubMed1987

Arm position as a source of error in blood pressure measurement.

The present study was designed to assess the value of correct positioning of a patient's arm when measuring blood pressure (BP). A total of 181 subjects were examined, 141 hypertensives on treatment, 25 untreated hypertensives, 15 normotensives. All the subjects underwent three BP measurements after a 5-min resting period in supine position. Then two BP readings were recorded in standing position with the arm either positioned by the patient's side or supported passively at patient's heart level. Average systolic BP (SBP) in standing position were 144.6 +/- 20.2 mmHg with the arm at the side and 136.4 +/- 21.1 mmHg with the arm at the heart level (p less than 0.001); average diastolic pressures were 99.0 +/- 12.0 mmHg and 90.2 +/- 12.3 mmHg (p less than 0.001), respectively. A fall in SBP greater than or equal to 20 mmHg from the supine to the upright position was detected in 18.2% of cases when measurement was performed at heart level; such a reduction was inapparent in two-thirds of cases when the arm was placed at the patient's body side. Incorrect positioning of a patient's arm during BP measurements in standing position leads to overestimation of BP values and masks the presence of postural hypotension.

Adult↗
PubMed1994

Light scatter based lymphocyte gate--helpful tool or source of error?

During flow cytometric analysis of 29 samples of human peripheral blood mononuclear cells, we observed that a light scatter-based lymphocyte gate would fail to cover all TCR (CD3)-expressing cells. A mean of 7.9 +/- 5.3% of all CD3+ cells was found outside the gate. In addition, this shifted cell subset showed an altered CD4/CD8 ratio (8.1 +/- 5.0% of all CD4+ and 13.7 +/- 5.8% of all CD8+ cells). The use of standard light scatter-based lymphocyte gates in acquisition and/or analysis of flow cytometry (FCM) data may thus lead to erroneous results, particularly if T cells are to be studied.

Artifacts↗
PubMedDate not supplied

Color and conventional image-directed Doppler ultrasonography: accuracy and sources of error in quantitative blood flow measurements.

Accuracy of two systems--conventional (DRF 400, Diasonics) and color-coded (Angiodynograph, Quantum/Phillips) image-directed Doppler ultrasonography--was investigated using an in vitro model that generated both monophasic and triphasic pulsatile flow patterns. Estimated and actual blood volume flow rates showed good correlations, but the sampling with a hand-held transducer led to wide variations in measurement error for the conventional (-69.2% to 50%) and the color-coded (-79.3% to 265.7%) systems. By performing multiple measurements, one could improve accuracy considering only the maximal values of a series instead of the mean values. Accuracy was impaired by interposed muscular or fatty tissue due to false low time-average velocity measurements caused by a loss of Doppler signal. Comparison of both systems revealed significant differences between pulsatility index values (p less than 0.001), blood flow velocities (p less than 0.001), and blood volume flow rates (p less than 0.05 for program flow, p less than 0.001 for manual and automatic flow program of the color-coded system).

Blood Flow Velocity↗
PubMed1982

Sources of error in the diagnosis of Guillain-Barre syndrome.

A careful monitoring of the accuracy of diagnosis in six cases of Guillain-Barre syndrome has shown that a substantial proportion of these patients initially diagnosed as having Guillain-Barre syndrome on the basis of characteristic clinical findings and an elevated level of protein in the spinal fluid had a neuropathy caused by another etiology. The pitfalls in the laboratory and clinical diagnosis of disorders that were confused with Guillain-Barre syndrome were several: the pattern of neurological dysfunction in the Guillain-Barre syndrome was not unique to that disorder; no specific laboratory test existed to confirm the diagnosis of Guillain-Barre syndrome; and the laboratory diagnosis of other causes of similar neurological disorders (especially heavy metal intoxication) depended upon tests that are very unreliable.

Adult↗
PubMed1986

Endogenous thymidine and hypoxanthine are a source of error in evaluating methotrexate cytotoxicity by clonogenic assays using undialyzed fetal bovine serum.

None of 13 fresh human tumor samples of various histology cloned in a two-layer agar culture system with 20% undialyzed fetal bovine serum (FBS) showed sensitivity to three antifolates, methotrexate (MTX), trimetrexate and 5,8-dideazaisofolic acid (IAHQ), even after continuous exposure to the highest concentrations (100 microM) for 21 days. In order to investigate this lack of antifolate drug effect, we compared the toxicity of continuous MTX exposure in the human colon carcinoma cell line HCT-8, cloned in a thymidineless medium (RPMI 1640) supplemented with 10% horse serum (HS), 10% fetal bovine serum (FBS), 20% FBS or 20% dialyzed FBS. In the presence of native FBS, when the minimum clone size was set at 30 cells/colony, the survival of HCT-8 cells reached a plateau at approximately 60% of untreated control after exposure to MTX concentrations between 0.1 microM and 100 microM. Only when the minimum clone size was set at 2 X 10(3) cells/colony was the sensitivity of HCT-8 cells to the antimetabolite comparable to that obtained in HS or dialyzed FBS (ED50 values in the range of 0.01 microM). MTX protection experiments indicated that even very small concentrations of thymidine and hypoxanthine together were sufficient to reproduce the pattern of sensitivity to MTX observed under culture conditions with undialyzed FBS. We conclude that for a proper evaluation of MTX cytotoxicity in clonogenic assays, dialyzed FBS and thymidine-less media should be employed; if native FBS is an absolute requirement for growth, only very large colonies (at least 10 cell divisions) should be scored.

Adenocarcinoma↗
PubMed1984

Possible sources of error in the calculation of ferrokinetic parameters using Ricketts' triexponential model.

The triexponential model developed by Ricketts et al. in 1975 for the calculation of ferrokinetic parameters has been widely used to obtain quantitative information about effective and ineffective erythropoiesis. However, a calculation error in one of the formulae of this method may have a considerable effect on those results which depend on the value of the third exponential constant, gamma 3. Moreover, the analysis of plasma 59Fe activity needs to be based on good counting statistics, which lambda-counting seldom provides after the first 24 h; therefore, 59Fe beta-counting is considered to be the best method.

Anemia↗