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At least 1,495 records · Page 83Linked to original sources
PubMed1977

Collaborative testing of a gas chromatographic charcoal tube method for seven organic solvents.

The National Institute for Occupational Safety and Health has undertaken a program to provide reliable sampling and analytical methods for a number of industrial hygiene uses. Recommendation of methods to the Department of Labor for compliance testing and inclusion of methods in critera for Recommended Standards for Occupational Exposures are two prime areas of utilization. This paper presents the results of our initial efforts in collaborative testing. The method is a charcal tube sampling procedure and a gas chromatographic analytical technique. Samples of seven single component solvents which included benzene, carbon tetrachloride, chloroform, dioxane, ethylene dichloride, trichloroethylene, and xylene along with two solvent mixtures which consisted of a benzene-xylene combination and an ethylene dichloride-trichloroethylene conbination were tested in two phases by 15 participating laboratories. The data analysis indicates the overalll error associated with the method and identifies sources of error within each segment of the method.

Benzene↗
PubMed1994

Idiosyncratic errors in visually directed reaching.

Subjects reaching with their eyes closed to visually presented targets missed their targets by an average of 4% of arm length; significant variation in the direction and magnitude of error arose from target location and idiosyncratic sources. The errors were largely unaffected by extreme variation in the arm's starting location. These data lend support to models of sensorimotor learning that focus on associations between postures and hand locations, but do not confirm a leading example of the class, exemplified by Kuperstein's (1988) circular reaction model.

Journal Article↗
PubMed2002

Study of a selection of 10 historical types of dosemeter: variation of the response to Hp(10) with photon energy and geometry of exposure.

An international collaborative study of cancer risk among workers in the nuclear industry is tinder way to estimate direetly the cancer risk following protracted low-dose exposure to ionising radiation. An essential aspect of this study is the characterisation and quantification of errors in available dose estimates. One major source of errors is dosemeter response in workplace exposure conditions. Little information is available on energy and geometry response for most of the 124 different dosemeters used historically in participating facilities. Experiments were therefore set up to assess this. using 10 dosemeter types representative of those used over time. Results show that the largest errors were associated with the response of early dosemeters to low-energy photon radiation. Good response was found with modern dosemeters. even at low energy. These results are being used to estimate errors in the response for each dosemeter type, used in the participating facilities, so that these can be taken into account in the estimates of cancer risk.

Calibration↗
PubMed1997

Is the Felsenstein zone a fly trap?

Although long-branch attraction, the incorrect grouping of long lineages in a phylogeny because of systematic error, has been identified as a potential source of error in phylogenetic analysis for almost two decades, no empirical examples of the phenomenon exist. Here, I outline several criteria for identifying long-branch attraction and apply these criteria to 18S ribosomal DNA (rDNA) sequence data for 13 insects. Parsimony and minimum evolution with p distances group the two longest branches together (those leading to Strepsiptera and Diptera). Simulation studies show that the long branches are long enough to attract. When a tree is assumed in which Strepsiptera and Diptera are separated and many data sets are simulated for that tree (using the parameter estimates for that tree for the original data), parsimony analysis of the simulated data consistently groups Strepsiptera and Diptera. Analyses of the 18S rDNA sequences using methods that are less sensitive to the problem of long-branch attraction estimate trees in which the long branches are separate.

Animals↗
PubMed2000

Comparison of forced-choice and subjective probability scales measuring behavioral intentions.

Three surveys compared the accuracy of predictions based on forced-choice and subjective probability scales. The latter produced significantly more accurate election predictions and significantly reduced the percentage of undecided, or "Don't Know" responses, compared to forced-choice scales in all three surveys. Analysis indicates subjective probability scales decrease sampling error and confirms there is an inherent source of error in traditional forced-choice questions about voting intentions not attributable to sampling error. The results are discussed with respect to (1) sampling and measurement errors in forced-choice and subjective probability scales measuring behavioral intentions, (2) their practical application, and (3) cognitive theory, especially support theory.

Adolescent↗
PubMed1985

Statistical methods in anesthesia articles: an evaluation of two American journals during two six-month periods.

Simple criteria were used to evaluate the statistical analyses in 243 articles from two American anesthesia journals published in the latter six months of 1981 and 1983. Eighty-two percent of the articles reported the use of control measures and 37% reported randomization of treatment, where they were possible. Data were classified as nominal, ordinal, or interval; as independent or related samples; as two-sample or more-than-two-sample cases. The descriptive, inferential, and correlative tests used were evaluated for appropriate application and primary errors were identified. Nine percent of the 722 descriptive statistics had major errors, most of which were a description of ordinal data as though they were interval. The incidence of erroneous applications of 394 inferential statistical tests was 78%. Nearly three-quarters of the 308 primary inferential statistical errors involved either use of a test for independent samples on related data (and vice versa) or multiple applications of an uncorrected test to the same data. Only 4% of the 113 statistics of association were considered erroneous, most because the method was not identified. No differences were detected in the incidence of errors in either experimental design or statistical analysis across time or across the two anesthesia journals. Fifteen percent of the 243 articles in both journals at both times were without major errors in statistical analysis. Recognition of potential sources of error should make it easier for investigators to use experimental designs and statistical analyses appropriate to their needs.

Anesthesia↗
PubMed1985

[Frequent errors in neuro-otologic diagnosis].

A number of characteristic sources of error during the testing of vestibular function, originating from anamnesis, equipment and examination, are described. It is stressed that false-positive findings are often due to the influence of alcohol and that false-negative findings may be the result of tiredness or sedative drugs. With regard to the caloric test, it is recommended that water provides a better stimulus than air, and that the warm caloric stimulus is more valid than the cold caloric stimulus. Attention should be paid to the ENG-recorders, particularly to an adequate writing breadth, and to time constants. Different parameters in use for quantitative analysis of the intensity of vestibular reactions are discussed. If the findings are vague, repeated examination will often help to clarify matters. The regular use of Frenzel glasses is of great importance, since otherwise examination of the vestibular organs must be considered incomplete.

Alcohol Drinking↗
PubMed1990

The reliability of goniometric measurements of active and passive wrist motions.

A reliability study was conducted to determine (a) the intrarater and interrater reliability of goniometric measurement of active and passive wrist motions under clinical conditions and (b) the effect of a therapist's specialization on the reliability of measurement. Randomly paired therapists performed repeated measurements of active and passive wrist motions in 48 subjects who had been referred to one of four occupational therapy or hand management clinics for evaluation and treatment. The data were analyzed with an intraclass correlation coefficient. A posteriori data analyses were performed to determine the effects of identified sources of error on the reliability of measurement. The results indicated that measurement of wrist motion by individual therapists is highly reliable and that intrarater reliability is higher than interrater reliability for all active and passive motions. Interrater reliability was generally higher among specialized therapists for reasons not immediately apparent from this study. With the exception of pain, identified sources of error were found to have surprisingly little effect on the reliability of measurement.

Adult↗
PubMed1996

Empirical techniques for determining the reliability, magnitude, and pattern of neuropsychological change after epilepsy surgery.

PURPOSE: We assessed test-retest neuropsychological performance in patients with complex partial seizures to derive reliable change indices (RCIs) and regression-based norms for change, indices that may be helpful in assessing cognitive outcome after anterior temporal lobectomy. METHODS: Forty patients with complex partial seizures (CPS) who did not undergo epilepsy surgery were administered a comprehensive neuropsychological battery on two occasions. Their test-retest data were used to compute both RCIs and regression-based norms for change for each neuropsychological index. RCIs corrected for practice effects provide a confidence interval (CI) indicating the degree of performance change required to exceed the variability attributable to sources of error (e.g., practice, test-retest reliability). Regression-based norms for change also correct for several sources of measurement error and examine observed versus expected test-retest changes on a common metric, thereby facilitating determination of the degree and relative magnitude of change across cognitive domains. RESULTS: Mean changes in test-retest performance were generally modest, but were evident across several test measures. Our data indicate a considerable degree of individual variability in test-retest performance. CONCLUSIONS: RCIs and regression-based norms are complementary indexes and can be particularly useful in examining the test-retest performance of individual patients who undergo epilepsy surgery as well as in the more general investigation of cognitive outcome after epilepsy surgery.

Adult↗
PubMedDate not supplied

Observational precision in general practice data: a technique for analysis and audit.

Terminal digit preference is a well-known source of error in blood pressure measurements. This was demonstrated in general practice computer databases by conducting a routine search and constructing a frequency distribution of the 20 992 blood pressure readings using mathematical software for a personal computer. The charts produced have a practical application in providing an audit tool whereby nurses and doctors can be made aware of this source of error, providing an opportunity for improving measurement technique and developing more refined and realistic protocols for blood pressure management in general practice. The same principles may be applied to other measurements made in the GP consultation such as peak expiratory flow rate.

Blood Pressure Determination↗
PubMed2001

Effects of modeling errors and EEG measurement montage on source localization accuracy.

The location of an electrical source in the brain can be determined from the EEGs the source produces on the scalp by calculating the location of a source in a model of the head using the EEGs. Modeling errors produced by differences between the actual head and the head model cause localization errors (i.e., errors in the calculated location of the source). This is a study of the localization errors caused by modeling errors produced by the differences between two features of actual head geometry and a spherical head model. The two features are general nonspherical head shape and the brain pan (i.e., the very nonspherical lower surface of the brain cavity). This is also a study of the localization accuracy of different EEG measurement montages when these modeling errors are present. It has been found that general nonspherical head shape causes maximum localization errors of approximately 1 cm, and that these errors are not very dependent on source location or orientation, or EEG montage. The localization errors caused by the brain pan are generally larger: The maximum error is approximately 2 cm. These errors are very dependent on source location and orientation, and EEG montage. The largest errors occur for sources close to and pointing toward the brain pan surface. These errors also vary widely with montage: A referential montage with the reference point on the bottom of the model has the largest errors. Referential montages with reference points on the side or top of the model, an average reference montage, or a bipolar montage generally produce much smaller errors.

Electroencephalography↗
PubMed1996

CT-target determination in postero-ventral pallidotomy: a universal method. Technical note.

Stereotactic targeting of the postero-ventral pallidum (PVP) presents special challenges to the surgeon 1) The target is in intimate relation to the optic tract and the internal capsule. 2) Proper angulation of the trajectory is crucial to achieve optimal effects given the long craniocaudal extension of the PVP. 3) The PVP is difficult to identify on computerized tomography (CT): the border between the internal capsule and the pallidum is usually not apparent. Potential sources of error in target determination include: - angulation of the scanning plane in relation to the intercommissural plane; - projection of the reference points (anterior commissure/posterior commissure [AC/PC]) results in the foreshortened intercommissural line, affecting the Y co-ordinate; - small tilts between the CT gantry and the stereotactic frame affect determination of the X and Z co-ordinates. Correction of these sources of error is done with basic trigonometric algorithms. The authors have developed a rapid method of stereotactic co-ordinate calculation which avoids the need to perform error-prone calculations under the pressure of operating room conditions. 1) The frame is applied with its basal plane corresponding roughly to the orbito-meatal line. 2) Thin CT slices (2 mm increments) are obtained through the area of interest and the slices are printed. 3) The major reference points (Foramen of Monro, AC, PC) are identified and marked. The PC point is projected onto the film containing AC (or viceversa if the PC slice is caudal to AC). 4) The intercommissural distance is measured, and the true length is obtained from a correction graph. The Y co-ordinate is then calculated as 1/2 ICL + 2 mm [towards AC]. 5) The slice corresponding to the target [Z co-ordinate] is obtained from a correction graph that takes into consideration the gap [number of slices] between AC and PC. 6) The X co-ordinate is placed 20 to 22 mm from midline. A graph that takes into consideration the coronal tilt of the stereotactic frame in relation to the CT gantry allows for final corrections of the X and Z co-ordinates. This step-by-step simple method of co-ordinate calculation can be used with any CT-compatible stereotactic frame.

Brain Mapping↗
PubMed1991

Methodological aspects on flow and image cytometric nuclear DNA assessments in prostatic adenocarcinoma.

Controversies exist in the literature about the value of the results of cytometric nuclear DNA assessments of the parenchymal cells in prostatic adenocarcinoma. These controversies are most probably due to methodological sources of errors. If these are adequately paid attention to, and if the results of the cytometric DNA assessments are used only as a supplementary tool to the correct fundamental clinical and histopathological data, the cytometric DNA ploidy pattern of each tumour can definitely be a valuable variable in the malignancy grading also of prostatic adenocarcinomas. The best way to eliminate the inherent sources of errors of methodological nature is to use both FCM and ICM parallel.

Adenocarcinoma↗
PubMed2003

MRI indirect stereotactic targeting for deep brain stimulation in Parkinson's disease.

AIM: Stereotactic localisation of brain targets for functional neurosurgery might be obtained with different neuroimaging sources. Magnetic resonance (MR) might be of particular interest for its high definition of the various brain structures; unfortunately, magnetic field distortion and inaccuracy in imaging reproduction constrain the use of MRI in stereotactic surgery. METHODS: We present an experimental work devoted to the utilization of MRI in the targeting of the subthalamic nucleus for deep brain stimulation (DBS) in Parkinsonian patients. RESULTS: Experimental data were obtained after PVC phantom and fixed human brain measurements of the stereotactic coordinates of specific basal ganglia structures. Intrinsic and external sources of error and imaging distortion have been carefully corrected. Afterwards, 36 patients, operated for DBS in the subthalamus for Parkinson's disease (PD), have been investigated. MRI targeting proved to be clinically successful; comparing anatomical and neurophysiological findings, MRI targeting scattered from the neurophysiological targeting in a minority of cases. CONCLUSION: MRI targeting proved to be reliable for functional stereotactic surgery, pending careful and adequate quality control of the distortion and of the sources of error.

Aged↗
PubMed1997

False low pulse oximetry reading associated with the concomitant use of a peripheral nerve stimulator and an evoked-potential stimulator.

One of the sources of error in pulse oximetry readings is associated with an abnormal signal-to-noise ratio. The pulse oximeter distinguishes the light absorbance of arterial blood from that of other absorbers by differentiating between a constant component and a pulsating component. The pulsating component is almost exclusively the result of arteriolar bed pulsations. Because pulse oximetry is based on the assumption that arterial blood is the only pulsatile absorber, any other fluctuating phenomenon could constitute a source of error. We report a case in which a low pulse oximetry reading was associated with concomitant use of a pulse oximeter and a peripheral nerve stimulator on the same arm. Further tests conducted using a nerve stimulator and a sensory evoked potential stimulator with different amplitudes and frequencies confirmed the association and delineated the relationship between frequency and amplitude of stimulation and the degree of artificial desaturation. A theoretical explanation for this phenomenon is presented.

Electric Stimulation↗
PubMed2004

The effects of emotional salience, cognitive effort and meta-cognitive beliefs on a reality monitoring task in hallucination-prone subjects.

OBJECTIVES: A tendency to externalize internal information on reality monitoring tasks has been documented in psychiatric patients with hallucinations. Furthermore, previous studies suggest that factors such as the emotional salience of the material, cognitive effort and meta-cognitive beliefs are important contributory factors in this tendency to externalize internal information on reality monitoring tasks. However, few studies have investigated these aspects in hallucination-prone subjects. Also, these factors have never been examined simultaneously. In the following study we wished to examine the effects of emotional salience, cognitive effort and meta-cognitive beliefs on reality monitoring functioning in hallucination-prone subjects. DESIGN: Between-participants group design. METHOD: One hundred normal subjects were administered a reality monitoring task. Words were presented by the experimenter. After each word, subjects were asked to say the first word that came to their mind. Words varied in terms of emotional valence and cognitive effort (high cognitive effort for words requiring longer latency times to associate a word and vice versa). Following a delay, words were presented consisting of those already presented by the experimenter or the subject (old) and those never presented before (new). For each word, subjects were required to identify whether the word was old or new. If the word was identified as old, subjects were required to identify the source of the word (subject or experimenter). Subjects also completed a questionnaire assessing meta-cognitive beliefs. RESULTS: Subjects were grouped according to their scores on a revised and elaborated version of the Launay-Slade Hallucinations Scale (LSHS). Those with scores within the top 25% were included in the hallucination-prone group (HP) (N = 25), whereas scores within the lower 25% were included in the non-hallucination-prone group (NHP) (N = 25). Results showed that the HP subjects had significantly more source discrimination errors than NHP subjects for self-generated items. In other words, HP subjects tended to misattribute to the experimenter items that they had produced themselves. This pattern was especially marked with emotionally charged material and with words that required more cognitive effort. In addition, HP subjects scored significantly higher on a scale assessing meta-cognitive beliefs compared with NHP subjects. Finally, scores on a scale assessing meta-cognitive beliefs were positively associated with source discrimination errors. CONCLUSIONS: These results suggest that cognitive effort, emotional salience and meta-cognitive beliefs all play a prominent role in the externalizing bias in hallucination-prone subjects. The results also provide evidence for the validity of the idea of a continuity between hallucination-prone subjects and psychotic patients with hallucinations on reality monitoring tasks, including a number of contributing factors in the occurrence of hallucinations.

Adult↗
PubMed2004

Comparative methods based on species mean values.

Comparative methods that use simple linear regression based on species mean values introduce three difficulties with respect to the standard regression model. First, species values may not be independent because they form part of a hierarchically structured phylogeny. Second, variation about the regression line includes two sources of error: 'biological error' due to deviations of the true species mean values from the regression line and sampling error associated with the estimation of these mean values [B. Riska, Am. Natural. 138 (1991) 283]. Third, sampling error in the independent variable results in an attenuated estimate of the regression slope. We consider estimation and hypothesis testing using two statistical models which explicitly justify the use of the species mean values, without the need to account for phylogenetic relationships. The first (random-effects) is based on an evolutionary model whereby species evolve to fill a bivariate normal niche space, and the second (fixed-effects) is concerned with describing a relationship among the particular species included in a study, where the only source of error is in the estimation of species mean values. We use a modification of the maximum-likelihood method to obtain an unbiased estimate of the regression slope. For three real datasets we find a close correspondence between this slope and that obtained by simply regressing the species mean values on each other. In the random effects model, the P-value also approximates that based on the regression of species mean values. In the fixed effects model, the P-value is typically much lower. Simulated examples illustrate that the maximum-likelihood approach is useful when the accuracy in estimating the species mean values is low, but the traditional method based on a regression of the species mean values may often be justified provided that the evolutionary model can be justified.

Acer↗
PubMed1997

Reliability of an image analysis system for quantifying the radiographic trabecular pattern.

A reliability evaluation technique was used to examine the reliability of an image analysis system of the trabecular pattern and to determine the contribution of three possible sources of error variance. Two series of radiographs were taken of 14 lumbar vertebral slices (28 radiographs). Every radiograph was placed on a viewing box for digitization four times by a single operator (112 positions of radiographs) and from every position of a radiograph an area of 15 mm x 15 mm was digitized twice (224 samples for analysis). Ten geometrical characteristics of the trabecular pattern were studied and its orientation was analyzed in 12 directions. Reliability was determined by calculating Cronbach's alpha. This design enabled dividing the measurement error (1-alpha) into fractions associated with the X-ray procedure, the operator and the system. Using this reliability evaluation technique, it was found that the orientation variables are more reliable than the geometric variables. It was found that effort to increase the reliability should be directed toward improving the technical procedure of this image analysis system. Also, repeated measurements will increase the reliability. The number of repeated measurements based on a desired reliability can be calculated. This procedure of evaluation gives the opportunity to select a source of error variance which have to be reduced to increase reliability most effectively.

Adult↗