[The 9th revision of the International Classification of Diseases--problems and sources of errors in the use of the new documentation of causes of death].
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Death Certificates↗
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Bone density measured by photon scattering. II. Inherent sources of error.
The origins of inherent sources of error in results of measurements of bone density by a photon scattering technique are described and their effects are predicted theoretically. The predictions are confirmed experimentally. The prime source of error is multiple scattering. A procedure has been developed to correct the observed densities for effects of multiple scattering.
Bone Diseases↗
Interobserver variability. A source of error in obstetric ultrasound.
Several sources of error encountered in obstetrical ultrasound examination have been analyzed from a computerized ultrasound database. The variability in measuring fetal landmarks and visualization of fetal structures were found to be significantly different among three registered sonographers who examined 1,410 consecutive second and third trimester patients. The rate of successful measurement of biparietal diameter (BPD) and average abdominal diameter (AAD), as well as successful visualization of fetal stomach and/or kidneys were statistically different among the three sonographers. Only the fetal femur length was consistently measured by all three sonographers. The bias in terms of actual millimeters measured was significantly different for both BPD and AAD. The bias related to the BPD was in the magnitude of 1 mm, while the bias related to the AAD was almost 3 mm. The clinical significance of these findings and the value of the computer to perform periodic checks to assure quality control in a busy ultrasound service are discussed.
Diagnostic Errors↗
Optimal interelectrode distance with the method of source density analysis.
Three error sources which contribute to the total error of the second space derivative (SSD) used with the method of current source density analysis (CSD) were examined. The approximate formula usually used with CSD was the first error source. Another error originated from the finite interelectrode distance. The measurement error of the device with which the potential was recorded was the third error source herein considered. A relative SSD error was determined to estimate the effect of the errors examined. The experimental data (a section from the three-dimensional potential profile in annuran cerebellum produced by parallel fiber activation) were fitted by polynomials, Fourier expansion and cubic splines. Then a preferable interelectrode distance was obtained corresponding to the minimal relative error.
Animals↗
[Sources of error in automated static perimetry].
Several sources of errors in interpreting computerized visual fields (learning effect, miotic pupil, sub-optimal refraction, dirty contact lenses, inadequate patient cooperation, anatomical obstacle, and choice of the wrong program) are described with the help of examples. Their identification should result in more reliable diagnoses.
Contact Lenses↗
Identification of the major sources of error in estrogen receptor measurements for individual laboratories using both tissue and cytosol samples.
The major sources of error between laboratories performing estrogen receptor measurements in tissue samples were identified for 17 participating laboratories in a trial conducted by the Australasian Quality Assurance programme. Both tissue and cytosol samples were provided, and the In-House assays were compared with the ER-EIA kit (Abbott Laboratories, U.S.A.) as a reference assay. For both the In-House and Abbott assays, tissue samples resulted in a between laboratory CV of about 55% and a within laboratory CV of about 30%. In contrast to tissue samples, the between laboratory CV for cytosol samples was reduced to 41% for the In-House assays and to 33% for the Abbott assay, whereas the within laboratory CV was reduced to 10% for both types of assay. The different methods of tissue homogenization by themselves were not found to be sources of error, and protein extraction efficiency from tissue was strongly correlated with protein measurement (P less than 0.0005). The major sources of error due to protein measurement, cytosol preparation, In-House and Abbott assays were evaluated for individual laboratories. The results indicated absence of any major sources of error for four laboratories, while one, two and three or more sources were indicated for seven, three and three laboratories respectively. The conclusion that about half the participants need to improve their ER assays was confirmed by three independent reviews. Furthermore, the trial demonstrated that tissue samples are essential as quality assurance material for a realistic assessment of ER assays in biopsy specimens.
Animals↗
The measurement of distortion: theoretical considerations.
When very find measurements are recorded for the purpose of establishing distortion values, from the standpoint of accuracy, specific procedures must be developed. In the procedural system defined here, a potential major source of error is indicated and the means of overcoming this error established. From the standpoint of modern electronic technology, the use of an analogue-to-digital interface with a digital computer is considered extremely advantageous and allows the utilization of technical help to carry out the preliminary measurements. Under these circumstances, major error sources, such as reader error and calculation error, are eliminated. Further, multiple readings on each point can be made without significant sacrifice of time. This latter statement can help define the reading accuracy on each point and allows an immediate further set of readings on any point that has a large variation in the initially established set of readings. The applicability of this approach to any system in which an accurate set of readings is required to define distortion or some other parameter is limited only by the imagination of the investigator. Measuring points can be established at any desired location, and the number required is a function of the mathematical analysis being attempted. The use of a digital computer to compute the final values allows an immediate remeasurement of the initial values if necessary, since the computer response time is of the order of seconds for the calculations carried out. This is very important if changes in the experimental setup are likely to occur with time. In general, a computerized scheme such as is proposed here allows the investigator to concentrate on the experiment rather than the calculation of results. Also, the use of technical help to carry out delicate measuring procedures can allow the investigator more time to analyze the final results.
Analog-Digital Conversion↗
Potential sources of errors in cation-exchange chromatographic measurement of plasma taurine.
We examined the potential sources of error in automated cation-exchange chromatographic quantitation of plasma taurine, both in sample preparation and in the analysis. Principal sources of error include: use of serum instead of plasma, which produces gross overestimates; use of tripotassium ethylenediaminetetraacetate (EDTA) as anticoagulant in systems involving ninhydrin detection (a ninhydrin-positive contaminant of EDTA emerges coincident with taurine); contamination with platelets; and placing volumes exceeding 20 microL on the cartridge used in the Technicon TSM Amino Acid Analyzer. We arrived at a simple technique in which we use EDTA as anticoagulant, micropore filtration to produce platelet-free plasma, and o-phthalaldehyde as the detection reagent for the sensitivity required to measure accurately the low concentration of taurine in plasma.
Autoanalysis↗
Abstinence from smoking and expired-air carbon monoxide levels: lactose intolerance as a possible source of error.
We investigated a possible source of contamination of expired-air carbon monoxide (CO) readings on CO monitors from raised expired-air hydrogen (H2) levels, namely lactose intolerance, the norm in certain ethnic groups. A significant correlation between expired-air CO and H2 readings was observed in four non-smoking lactose maldigesters.
Breath Tests↗
Optical radiation measurements: instrumentation and sources of error.
Accurate measurement of optical radiation is required when sources of this radiation are used in biological research. The most difficult measurements of broadband noncoherent optical radiations usually must be performed by a highly trained specialist using sophisticated, complex, and expensive instruments. Presentation of the results of such measurement requires correct use of quantities and units with which many biological researchers are unfamiliar. The measurement process, physical quantities and units, measurement systems with instruments, and sources of error and uncertainties associated with optical radiation measurements are reviewed.
Optics and Photonics↗
Sources of error in intraocular lens power calculation.
The hypothesis that the minimum error in predicted refraction after implantation of an intraocular lens (IOL) of calculated power is the sum of the random error in (1) the measurement of the axial length, (2) the measurement of the corneal power, and (3) the estimation of the pseudophakic anterior chamber depth (ACD) is proposed. Based on preoperative and postoperative biometry of 584 IOL implantations, 54% of the error was attributed to axial length errors, 8% to corneal power errors, and 38% to errors in the estimation of the postoperative ACD, when a fixed ACD was used in the IOL calculations. However, if the ACD was predicted according to a previously described regression method, the contribution of error from the ACD source was reduced to 22%, thereby reducing the total refractive prediction error from +/- 1.03 diopters (D) (+/- SD) to +/- 0.92 D (+/- SD). These predictions accord with clinical results.
Adult↗
Cell adherence as a serious source of error in the haemacytometer count of leucocytes in artificial suspensions.
This report demonstrates a previously disregarded source of error in the count of lymphocytes that have been fixed in Turk's dilution fluid (acetic acid and gentian violet). If the dilution fluid does not contain any serum protein or other proteins, a large proporation of the lymphocytes will stick to the walls of the mixing vessel. The use of plastic or siliconized vessels does not prevent this. The number of cells which in that way will be eliminated from the suspension is dependent on several variables, such as the type of mixing procedure and mixing vessel, the compensation of the dilution fluid and the cell density. As a consequence it is difficult to give any correction factor for such a count in a haemacytometer counting chamber. More than 30% of the cells may disappear under generally obtained conditions. This source of error is to some extent also involved in the white blood cell count, despite the presence of about 1% protein in the dilution fluid from the serum and lysed erythrocytes. To prevent this loss of cells either bone serum albumin, to a concentration of 5%, or the detergent Certrimide, to a concentration of 2-5 mM, may be added to the dilution fluid.
Animals↗
The effects of measurement errors in the plasma radioactivity curve on parameter estimation in positron emission tomography.
The effects of three error sources in plasma curve measurements on parameter estimation in kinetic analysis of positron emission tomography (PET) fluorodeoxyglucose (FDG) data are investigated by computer simulation. The three error sources are: (1) measurement noise in the radioactivity concentrations of plasma samples; (2) linear interpolation between adjacent plasma sampling points of the plasma time activity curve; and (3) incorrect weights used for the least-squares regression. All three error sources are found to increase the variability of the parameter estimates, with the first one a primary error source in normal PET FDG studies. The performance of five estimation methods which account for the error sources are evaluated. When the noise variances of the plasma and the tissue measurements are not known, an iterative weighting procedure is shown to give accurate and reliable estimates.
Computer Simulation↗
Sources of error in recording the blood pressure of patients with hypertension in general practice.
Sources of error in recording the blood pressures of patients with hypertension in general practice were examined for 1072 patients over two and a half years. A highly significant preference for terminal digit 0 was shown, but terminal digit preference operates in a different manner around important thresholds. Doctors did not adhere consistently to the protocol that they accepted. These sources of bias affect the calculations of mean blood pressure and have considerable implications for decisions about treatment for many patients.
Adult↗
[Regulative resistances during mouth breathing--a source of error determining nasal resistance by pulmonary function tests (author's transl)].
Methods to determine airway resistance - pulmonary function tests - have been recommended for the measurement of nasal resistance. Using the "oscillation method", you can demonstrate in some patients a source of error: Some mouth breathers can have an additional regulative resistance. By means of direct write-out tracings it is demonstrated that the simple subtraction of the resistances (during mouth and nose breathing respectively) is not a reliable method to determine nasal resistance. But the source of error can be recognized using a more luxurious measuring technique.
Airway Resistance↗
[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↗
Constant force probing with and without a stent in untreated periodontal disease: the clinical reproducibility problem and possible sources of error.
There is presently no satisfactory method of detecting periodontal disease activity at a specified site by means of clinical measurements. This study was designed to examine the possible sources of error with regard to probing measurement reliability. Intra-examiner reproducibility of probing measurements was studied at 766 sites in 10 patients with untreated periodontitis, using a 0.25 N hinged constant force probe (a) with a stent for guidance and landmark, and (b) without stent. The stent made little difference to overall reproducibility of probing depths, though it appeared to reduce variation in different areas. Repeated probing led to an increase in some measurements, perhaps by an effect on tissues. Reproducibility of probing depth was lower in deep pockets, and about 2% of all probing depth scores varied by 3 mm or more at the same site. 4 possible sources of measurement error were noted: visual and tactile observational error, positional error and tissue change. The results are discussed in relation to the clinical detection of periodontal disease activity.
Diagnostic Errors↗
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↗