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At least 109 records · Page 6Linked to original sources
PubMed2001

Source of errors in the evaluation of early rectal cancer by endoluminal ultrasonography.

PURPOSE: Although preoperative evaluation of early rectal cancers can be done by endoluminal sonography and by means of colonoscopic findings, it is still controversial whether endoluminal sonography can effectively discriminate mucosal from submucosal lesions. This study was performed to verify objective causes of errors in the evaluation of early rectal cancer (T0/1) using a review of videotaped endoluminal sonography images. METHODS: Eighty-nine patients with suspected early rectal cancer on endoluminal sonography were included. Two different scanners with appropriate probes were used according to tumor location, i.e., transrectal ultrasonography was used to scan up to 8 cm of the rectum above the anal verge, whereas endoscopic ultrasonography was used to assess higher lesions. Endoluminal sonography images were correlated with histologic infiltration and were reevaluated carefully to identify sources of errors. RESULTS: Sensitivity and specificity were 83.1 and 96.5 percent, respectively, for tumor staging, whereas sensitivity was very low compared with specificity (16.7 vs. 90.2 percent) for metastatic lymph nodes. Endoluminal sonography images showed irregularity of the underlying tumor border (P < 0.01) and hypoechoic blurring or cutoff of the inner and outer hypoechoic layers (P < 0.001), all of which closely correlated with histologic infiltration of tumor cells. Overstaging occurred more than twice as often as understaging in tumor reevaluation (14 vs. 5 occurrences). In contrast to tumors, lymph nodes showed a similar amount of both overstaging (four cases) and understaging (five cases). The sources of errors were summarized as five types: false instrumentation, interpretive errors, anatomic defects, imaging failure, and inevitable errors. CONCLUSIONS: Because false instrumentation, interpretive errors, and anatomic defects were considered preventable, 23 (82.1 percent) of the 28 errors might have been avoided. Therefore, a clear image by endoluminal sonography can effectively distinguish mucosal from submucosal lesions in early rectal cancer.

Diagnosis, Differential↗
PubMed1987

[Noninvasive measurement of cardiac output using two-dimensional Doppler echocardiography and analysis of sources of error].

The purpose of this study was (1) to analyze the factors responsible for errors in the two-dimensional Doppler echographic measurements of cardiac output (C.O.) and (2) to establish a noninvasive method for measuring C.O. The subjects were 50 cardiac patients who had neither aortic valve disease nor intracardiac shunts. The C.O. was calculated using the following formula: C.O. (l/min) = mean flow velocity (cm/sec) x pi(aortic ring diameter/2)2 (cm2) x 60/10(3) Left ventricular ejection flow velocity was recorded in the center of the aortic ring from the apical approach. Mean velocity was calculated by integration of instantaneous mean velocity in the ejection phase divided by the cardiac cycle length, and was corrected by the Doppler incident angle. The inner diameter of the aortic ring was measured in the parasternal long-axis view at the time of the maximum ejection flow velocity. The following results were obtained: 1. Sources of error in the measurement of cardiac output. 1) Accuracy of instantaneous mean velocity calculating circuit: This calculating circuit was accurate in model experiments using pulsatile flow. 2) Effect of high-pass filter: In model circuits, application of high-pass filter overestimated flow velocity. The higher the cut-off frequency of the high-pass filter, the larger the overestimation. This was probably due to the parabolic flow velocity profile in the circuit. 3) Flow velocity profile in the aortic ring: The flow velocity profile seemed to be flat in the aortic ring except near the anterior aortic wall. Therefore, the effect of the high-pass filter was considered to be negligible in case of clinical application. 4) The effects of shift and size of sample volume: The location of sample volume relative to the aortic valve ring shifted about 7 mm during systole. However, the shift and size of sample volume seemed to have little effect on the measured C.O., because the flow velocity profile was nearly flat in the aortic ring. 5) Ultrasound beam incident angle: From a practical viewpoint, it was necessary to set an incident angle of less than 50 degrees for minimizing the error. We were able to set the angle within 50 degrees in all but one of patients. 6) Diameter of the aortic ring: Two-dimensional echographic measurement of the aortic ring diameter was not so accurate; it seemed to become a major source of error in the calculation of C.O.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
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↗
PubMed2005

Precision and variance components in quantitative gel electrophoresis.

The error in quantitative gel electrophoresis/Western blotting was investigated considering the purity testing of erythropoietin. The overall error was over 35% relative standard deviation. However, an analysis of variance elucidated that the interoperator variability was the dominant error source, which already explained almost 80% of the total variance. Careful compilation and investigation of the possible error sources strongly indicates that the immunoreaction after blotting and the subsequent color reaction are the major error sources in this case.

Analysis of Variance↗
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↗
PubMed2005

Triphasic MRI of pelvic organ descent: sources of measurement error.

PURPOSE: To identify sources of error when measuring pelvic organ displacement during straining using triphasic dynamic magnetic resonance imaging (MRI). MATERIALS AND METHODS: Ten healthy nulliparous woman underwent triphasic dynamic 1.5 T pelvic MRI twice with 1 week between studies. The bladder was filled with 200 ml of a saline solution, the vagina and rectum were opacified with ultrasound gel. T2 weighted images in the sagittal plane were analysed twice by each of the two observers in a blinded fashion. Horizontal and vertical displacement of the bladder neck, bladder base, introitus vaginae, posterior fornix, cul-de sac, pouch of Douglas, anterior rectal wall, anorectal junction and change of the vaginal axis were measured eight times in each volunteer (two images, each read twice by two observers). Variance components were calculated for subject, observer, week, interactions of these three factors, and pure error. An overall standard error of measurement was calculated for a single observation by one observer on a film from one woman at one visit. RESULTS: For the majority of anatomical reference points, the range of displacements measured was wide and the overall measurement error was large. Intra-observer error and week-to-week variation within a subject were important sources of measurement error. CONCLUSION: Important sources of measurement error when using triphasic dynamic MRI to measure pelvic organ displacement during straining were identified. Recommendations to minimize those errors are made.

Adolescent↗
PubMed2005

How to improve quality assurance in fluorometry: fluorescence-inherent sources of error and suited fluorescence standards.

The scope of this paper is to illustrate the need for an improved quality assurance in fluorometry. For this purpose, instrumental sources of error and their influences on the reliability and comparability of fluorescence data are highlighted for frequently used photoluminescence techniques ranging from conventional macro- and microfluorometry over fluorescence microscopy and flow cytometry to microarray technology as well as in vivo fluorescence imaging. Particularly, the need for and requirements on fluorescence standards for the characterization and performance validation of fluorescence instruments, to enhance the comparability of fluorescence data, and to enable quantitative fluorescence analysis are discussed. Special emphasis is dedicated to spectral fluorescence standards and fluorescence intensity standards.

Journal Article↗
PubMed1984

The inaccuracy of total uterine volume measurements: sources of error and a proposed solution.

Inaccuracies in total intrauterine volumes calculated using the prolate ellipse equation have been reported. No previous study has examined all the sources of error. In this study, a comprehensive approach was undertaken. Measurements were obtained from scans of the pregnant uterus in the prone position using an automated water-path scanner (Octoson) and in the supine position using standard static B-mode scanners. Several conclusions could be drawn: 1) From the Octoson prone scans, uterine volumes obtained using the prolate ellipse formula were markedly different from the true uterine volumes obtained by the summation of stepped areas. This showed that the prolate ellipse formula was inaccurate. 2) From the static supine scans, many observer inconsistencies were found in uterine volumes obtained from the prolate ellipse formula. This made the prolate ellipse formula unreliable. 3) Previously published graphs calculated from the prolate ellipse equation, comparing fetal age with total intrauterine volume, were found to vary accuracy, presumably as a result of 1 and 2. A more accurate approach is proposed. Using the outer uterine wall as the boundary, the stepped area-to-volume values of transverse scans taken at 3-cm intervals were found to closely approximate true volumes, with an average error of only 3.5 per cent. Since these measurements encompass the intrauterine contents and the myometrium, it is suggested that the term "total uterine volume" be used instead of "total intrauterine volume."

Amniotic Fluid↗
PubMed2003

Sources of error in delayed payment of physician claims.

BACKGROUND AND OBJECTIVES: Our objectives were to determine the distribution of errors and estimate the magnitude of the burden of delayed payments in a large physician group practice. METHODS: A 25% random sample (n=775) was taken from all billed records of a physician group practice in the Pacific Northwest that were delayed 6 months or more as of June 30, 2001. The source and specific reasons for payment delays, as well as the amount of each unpaid invoice, were determined by electronic documentation or telephone calls to the payor. Analysis of variance was used to determine whether the amount of the invoice was associated with the source and reason of error. RESULTS: The source of delayed payments due to provider, payor, patient, and technical error were 36.1%, 28.1%, 14.5%, and 21.3%, respectively. The most-frequent reasons for delayed payment were that the provider incorrectly set up the account (15.2%), the provider did not follow up on denial (12.9%), and the payor incorrectly processed the invoice (11.6%). Analysis of variance suggested that the invoice amount was not significantly associated with the source but was significantly different across reasons for delayed payment. The potential financial impact of earlier recovery of payment was $262,270. CONCLUSIONS: In these data, provider and payor errors accounted for almost two thirds of delayed payments. The most promising avenue for providers to reduce delayed payments is by reducing their own errors. Eliminating the two most common errors would result in a more timely recovery of nearly $70,000 in revenues.

Insurance, Health, Reimbursement↗
PubMed1994

The Canadian National Calibration Reference Centre for In-Vivo Monitoring. Part II: Sources of errors in thyroid monitoring of occupationally exposed personnel.

This article, the second of a five-part series covering various aspects of occupational thyroid monitoring, addresses the sources of error that can affect the final result obtained from thyroid monitoring, such as geometry effects (thyroid size, thyroid depth, precision and accuracy of the detector placement, and neck-detector distance). The article also suggests ways in which these errors can be minimized and identifies those errors that are difficult to quantify.

Adult↗
PubMed2002

A calibration approach to glandular tissue composition estimation in digital mammography.

The healthy breast is almost entirely composed of a mixture of fatty, epithelial, and stromal tissues which can be grouped into two distinctly attenuating tissue types: fatty and glandular. Further, the amount of glandular tissue is linked to breast cancer risk, so an objective quantitative analysis of glandular tissue can aid in risk estimation. Highnam and Brady have measured glandular tissue composition objectively. However, they argue that their work should only be used for "relative" tissue measurements unless a careful calibration has been performed. In this work, we perform such a "careful calibration" on a digital mammography system and use it to estimate breast tissue composition of patient breasts. We imaged 0%, 50%, and 100% glandular-equivalent phantoms of varying thicknesses for a number of clinically relevant x-ray techniques on a digital mammography system. From these images, we extracted mean signal and noise levels and computed calibration curves that can be used for quantitative tissue composition estimation. In this way, we calculate the percent glandular composition of a patient breast on a pixelwise basis. This tissue composition estimation method was applied to 23 digital mammograms. We estimated the quantitative impact of different error sources on the estimates of tissue composition. These error sources include compressed breast height estimation error, residual scattered radiation, quantum noise, and beam hardening. Errors in the compressed breast height estimate contribute the most error in tissue composition--on the order of +/-7% for a 4 cm compressed breast height: The spatially varying scattered radiation will contribute quantitatively less error overall, but may be significant in regions near the skinline. It is calculated that for a 4 cm compressed breast height, a residual scatter signal error is mitigated by approximately sixfold in the composition estimate. The error in composition due to the quantum noise, which is the limiting noise source in the system, is shown to be less than 1% glandular for most breasts.

Adipose Tissue↗
PubMed1998

Sources of error and nutritional adequacy of the food guide pyramid.

The authors assessed the accuracy of college students' use of the Food Guide Pyramid (FGP) in their diets and evaluated sources of error and nutritional adequacy of the pyramid. Students enrolled in an undergraduate nutrition class (N = 346) completed 3-day dietary records that were analyzed, using computer software, to determine individual recommended dietary allowance (RDA) values and the extent to which the students' diets met those values. The students' most common error in using the FGP was underestimating serving sizes. Only 8% of the students consumed the minimum recommended number of servings for all food groups, but diets that satisfied FGP recommendations also tended to satisfy RDA requirements. Less than 2% of the students who met the minimal number of FGP servings did not satisfy their RDA values, but less than 45% of the survey participants, regardless of gender or residence, met the recommended intake for dietary fiber. The FGP was judged to be a good indicator of dietary adequacy.

Adolescent↗
PubMed1980

Sources of error in the determination of output voltage of pulse generators by pacemaker system analyzers.

The use of threshold or pacemaker system analyzers with widely different characteristics has introduced potential sources of error in the determination of the output voltage of pulse generators. This is further compounded by the availability of pulse generators with diverse waveform configurations and programmability capabilities. Because of this non-uniformity, the physician must have some rudimentary knowledge of waveform characteristics and appreciate the limitations of threshold or pacemaker system analyzers to avoid the unnecessary replacement of normally-functioning pulse generators.

Electric Power Supplies↗
PubMed1995

Clinical reasoning about new symptoms despite preexisting disease: sources of error and order effects.

BACKGROUND: Previous work that studied the evaluation of new, atypical symptoms in patients with preexisting diseases indicated that physicians largely ignored the past medical history and therefore erred in their diagnoses, when compared to a Bayesian analysis. Other studies have shown that the order in which information is presented to a decision maker can affect the inferences drawn, again contrary to a Bayesian standard. OBJECTIVES: The aim of the study was to investigate the source of disparity between clinical judgment and Bayesian analysis and to investigate the effect of alternative orders of presenting information on diagnostic conclusions. METHODS: Two groups of family physicians received a written clinical scenario. One group was given the past medical history before the history of present illness, the physical exam, and the laboratory data. The second group learned about the past medical history after all other clinical information had been presented. Judgments of test accuracy and probably diagnosis were collected at several points to identify the source of any diagnostic error. RESULTS: For both groups, the major source of error was in estimating the prior probability of disease, not in estimating the accuracy of a diagnostic test or updating opinions following receipt of test results. Although both groups of physicians received the same information, they came to markedly different conclusions about the most likely diagnosis. The group given the past medical history at the beginning of the scenario considered this information much less significant than did the group who received it at the end. CONCLUSIONS: Family physicians deviate from a Bayesian standard of reasoning by wrongly specifying prior probabilities and by being influenced by the order in which clinical information is presented.

Bayes Theorem↗
PubMed1996

End-tidal PCO2 monitoring via nasal cannulae in pediatric patients: accuracy and sources of error.

OBJECTIVE: To assess the correlation and accuracy of end-tidal PCO2 (PetCO2) sampled via nasal cannulae in pediatric patients by comparison to the criterion standard PaCO2, and to identify sources of error during PetCO2 monitoring via nasal cannulae. METHODS: PetCO2 was monitored continuously by sampling end-tidal gas through nasal cannulae that had been designed and manufactured for this purpose in spontaneously breathing children undergoing conscious or deep sedation during either cardiac catheterization (n = 43) or critical care (n = 54). When both the capnographic wave form and the PetCO2 value had been stable for at least 10 minutes, the PetCO2 value was recorded while blood was drawn from an indwelling arterial line for PaCO2 measurement. The effects of age, weight, respiratory rate, oxygen delivery system, airway obstruction, mouth breathing, and cyanotic heart disease were evaluated by linear regression analysis and calculation of absolute bias (PaCO2-PetCO2). RESULTS: Mouth breathing, airway obstruction, oxygen delivery through the ipsilateral nasal cannula, and cyanotic heart disease adversely affected accuracy. In patients without those factors, PetCO2 correlated well with PaCO2 (R2 = 0.994), and absolute bias was 3.0 +/- 1.8 mmHg. CONCLUSIONS: Several factors-some controllable and all recognizable-affect the accuracy of PetCO2 monitored via nasal cannulae in pediatric patients. When these factors are not present, PetCO2 correlates well with PaCO2 and appears to be a useful monitor of ventilatory status during conscious or deep sedation.

Carbon Dioxide↗
PubMed2003

[Sources of errors in blood glucose self-monitoring in 100 young diabetics].

Self-monitoring of blood glucose (SMBG) has become increasingly important in the treatment plan of people with diabetes. Identifying sources of error in SMBG can have a significant clinical impact. The objective of the present study was to evaluate the testing skills in diabetic children and adolescents. The study included 100 patients (46 females and 54 males) with an age of 8-18 years and a mean duration of diabetes of 4.5 years. They were autonomous for SMBG: an experienced diabetes nurse had taught earlier how to proceed. The daily frequency of SMBG was 4 in 79 patients, 3 in 11, and 2 in 10. The observations of their performance of blood glucose monitoring skills were done twice, during 2 consecutive visits at the diabetes clinic at a mean interval of 2 months. Each patient was observed by a specialized nurse who scored the child's testing behavior with an observation grid, according to 45 items. After the first observation, children and adolescents were given feedback on the identified errors. The second observation allowed scoring the improvements. During the first observation, nearly 90% of the patients made 3 or more mistakes, 69% more than 5, and 10% more than 10. During the second observation, these frequencies fall to 17, 2, and 0%. The main errors were the following (first vs second observation, in % of patients): not washing hands: 54 vs 3; incorrect setting for hour and date: 47 vs 2, and 17 vs 2; no knowledge of the meaning of "HI" (blood glucose > 500 or 600 mg/dL): 55 vs 3; no knowledge of the meaning of "LO" (< 10 or 20 mg/dL): 49 vs 1; insufficient blood drop: 19 vs 10. Younger children, with a shorter duration of diabetes and of autonomy for SMGB, need closer supervision. Errors were unrelated to frequency of SMBG, and glycated haemoglobin. To conclude, it is important to periodically assess diabetic children and adolescents' SMGB technique in order to correct the mistakes, mainly in younger children. The use of an observation grid allows an accurate analysis of the numerous possible errors.

Adolescent↗