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PubMedDate not supplied

Accuracy of prenatal diagnosis of congenital heart defects.

OBJECTIVES: (1) To evaluate the detection and accuracy of fetal echocardiography for congenital heart defects (CHD). (2) To compare the detection and accuracy of a team of maternal fetal medicine specialists and radiologists (MFM/R) with those of perinatal cardiologists (PC). METHODS: All fetal echocardiograms performed from 1/91 to 6/95 were reviewed retrospectively. CHD diagnoses made prenatally were compared with postnatally-confirmed diagnoses. RESULTS: 106 heat defects were correctly detected prenatally. There were 10 incorrect diagnoses, 6 false-negatives and 4 false-positives. Overall detection rate (sensitivity) was 95%, while overall accuracy was 87%. Detection rate for MFM/R and PC were 91 and 97%, respectively (p = 0.4). Accuracy was 74% for MFM/R and 92% for PC (p = 0.02). CONCLUSIONS: CHD can be identified reliably by prenatal echocardiography. The involvement of a PC in the prenatal diagnosis of these defects may improve diagnostic accuracy.

False Negative Reactions↗
PubMed1993

Accuracy and precision in vitro of Beetrode microelectrodes used for intraoral pH measurements.

The accuracy and precision of 12 different microelectrodes were assessed through a series of pH recordings of buffer solutions with known pH values. Some electrodes were quite accurate, yielding an average deviation of recordings from true values of about 0.05 pH units, while other electrodes yielded average deviations of up to 0.20 pH units. The precision of the electrodes also varied between electrodes. While all recordings were within 0.15 pH units from the true values for some electrodes, other electrodes showed a marked dispersion with less than 25% of the recordings being within 0.15 pH units from true values. For some electrodes accuracy depended on true pH values, while no such dependency was noted with respect to the precision of the electrodes tested. Both accuracy and precision may be impaired when pH recordings are made on solutions with pH values outside the pH range encompassed by the calibration buffers. Our results demonstrate that the accuracy and precision of these microelectrodes cannot be considered fixed and known parameters. Electrodes should therefore be checked prior to clinical use, and electrodes with low accuracy and precision should be excluded from further use.

Buffers↗
PubMed1983

Accuracy of volume determination by two-dimensional echocardiography: defining requirements under controlled conditions in the ejecting canine left ventricle.

The accuracy of two-dimensional echocardiographic left ventricular volume measurement in an isolated heart preparation was tested using Simpson's reconstruction of progressively fewer short-axis cross sections of known location. Echocardiographic images from five ejecting hearts submerged in a special tank were obtained under conditions designed for maximal accuracy of echocardiographic volume assessment. Echocardiographic determinations of 52 volumes at various times throughout the cardiac cycle were compared, by least-squares linear regression, with simultaneous direct-volume measurements by volumetric chamber (range 9.4-44.8 ml). Echocardiographic and direct measurements correlated well for all numbers of cross sections from 1-19 (r = 0.84-0.97); however, variability of direct volume predicted from a given echocardiographic measurement increased nonlinearly as the number of cross sections per heart decreased, and was especially large when three or fewer cross sections were used (SEE = 4.6-7 ml). The accuracy of echocardiographic measures was compared for each number of cross sections per heart, varying from one to 19; accuracy was defined as the mean absolute difference between echocardiographic and direct measurements of volume, ejection fraction, and maximal rate of ejection. The accuracy of echocardiographic measurements was significantly reduced with fewer than four cross sections per heart for ventricular volume, three cross sections for ejection fraction, and five cross sections for maximal rate of ejection. In light of what appears to be required for accurate echocardiographic volume measurement in this controlled, ejecting, noninfarcted, in vitro preparation, additional cross sections may be required in intact animals and human subjects, especially in those with diseases that cause ventricular asymmetry or regional dysfunction.

Animals↗
PubMed2004

Dissociating confidence and accuracy: functional magnetic resonance imaging shows origins of the subjective memory experience.

Successful memory typically implies both objective accuracy and subjective confidence, but there are instances when confidence and accuracy diverge. This dissociation suggests that there may be distinct neural patterns of activation related to confidence and accuracy. We used event-related functional magnetic resonance imaging to study the encoding of novel face--name associations, assessed with a postscan memory test that included objective measures of accuracy and subjective measures of confidence. We showed specific neural activity in the left inferior prefrontal cortex associated with trials when subjects expressed high confidence that they had chosen the correct name for the face and made a correct identification. Moreover, we found that this region was also associated with imparting high confidence when subjects chose the incorrect name. However, medial temporal lobe regions showed activity only for high-confidence correct trials. Many functional magnetic resonance imaging studies have shown that the medial temporal lobe and left prefrontal regions are particularly important for the successful formation of memories by using a combination of subjective and objective measures. Our findings suggest that these regions may be differentially involved in the objective and subjective components of memory and that the origins of confidence-accuracy dissociations may be related to incomplete activation of the neural pattern seen in successful encoding. These findings may also aid understanding of eyewitness misidentifications and memory distortions.

Adult↗
PubMed2003

Accuracy-based learning classifier systems: models, analysis and applications to classification tasks.

Recently, Learning Classifier Systems (LCS) and particularly XCS have arisen as promising methods for classification tasks and data mining. This paper investigates two models of accuracy-based learning classifier systems on different types of classification problems. Departing from XCS, we analyze the evolution of a complete action map as a knowledge representation. We propose an alternative, UCS, which evolves a best action map more efficiently. We also investigate how the fitness pressure guides the search towards accurate classifiers. While XCS bases fitness on a reinforcement learning scheme, UCS defines fitness from a supervised learning scheme. We find significant differences in how the fitness pressure leads towards accuracy, and suggest the use of a supervised approach specially for multi-class problems and problems with unbalanced classes. We also investigate the complexity factors which arise in each type of accuracy-based LCS. We provide a model on the learning complexity of LCS which is based on the representative examples given to the system. The results and observations are also extended to a set of real world classification problems, where accuracy-based LCS are shown to perform competitively with respect to other learning algorithms. The work presents an extended analysis of accuracy-based LCS, gives insight into the understanding of the LCS dynamics, and suggests open issues for further improvement of LCS on classification tasks.

Algorithms↗
PubMed2006

The quality of reporting of diagnostic accuracy studies in glaucoma using the Heidelberg retina tomograph.

PURPOSE: Scanning laser tomography with the Heidelberg retina tomograph (HRT; Heidelberg Engineering, Heidelberg, Germany) has been proposed as a useful diagnostic test for glaucoma. This study was conducted to evaluate the quality of reporting of published studies using the HRT for diagnosing glaucoma. METHODS: A validated Medline and hand search of English-language articles reporting on measures of diagnostic accuracy of the HRT for glaucoma was performed. Two reviewers selected and appraised the papers independently. The Standards for Reporting of Diagnostic Accuracy (STARD) checklist was used to evaluate the quality of each publication. RESULTS: A total of 29 articles were included. Interobserver rating agreement was observed in 83% of items (kappa=0.76). The number of STARD items properly reported ranged from 5 to 18. Less than a third of studies (7/29) explicitly reported more than half of the STARD items. Descriptions of key aspects of the methodology were frequently missing. For example, the design of the study (prospective or retrospective) was reported in 6 of 29 studies, and details of participant sampling (e.g., consecutive or random selection) were described in 5 of 29 publications. The commonest description of diagnostic accuracy was sensitivity and specificity (25/29) followed by area under the ROC curve (13/29), with 9 of 29 publications reporting both. CONCLUSIONS: The quality of reporting of diagnostic accuracy tests for glaucoma with HRT is suboptimal. The STARD initiative may be a useful tool for appraising the strengths and weaknesses of diagnostic accuracy studies.

Databases, Factual↗
PubMed2007

The effects of study design and spectrum bias on the evaluation of diagnostic accuracy of confocal scanning laser ophthalmoscopy in glaucoma.

PURPOSE: To assess the effects of study design and spectrum bias on the evaluation of diagnostic accuracy of confocal scanning laser ophthalmoscopy (CSLO) in glaucoma. METHODS: Analysis 1 included 67 eyes with glaucomatous visual field loss and 56 eyes of normal volunteers. Estimates of diagnostic accuracy in this analysis were compared to those obtained from analysis 2, which included a cohort of patients with suspected glaucoma, but without visual field loss at the time of CSLO imaging. For analysis 2, 40 eyes with progressive glaucomatous optic disc change were included in the glaucoma group and 43 eyes without any evidence of progressive damage to the optic nerve that were observed untreated for an average time of 9.01 +/- 3.09 years were included in the normal group. Areas under the receiver operating characteristic (ROC) curves (AUC) were used to evaluate diagnostic accuracy of CSLO parameters. RESULTS: There was a statistically significant difference between the performance of the parameter with largest AUC, discriminant function Bathija, in analysis 1 (AUC = 0.91) compared with its performance in analysis 2 (AUC = 0.71; P = 0.002). For the contour-line-independent parameter glaucoma probability score, a statistically significant difference was also observed in the performance obtained in analysis 1 (AUC = 0.89) compared with analysis 2 (AUC = 0.65; P < 0.001). CONCLUSIONS: Estimates of diagnostic accuracy of CSLO in glaucoma can be largely different depending on the population studied and the reference standard used to define disease. Diagnostic accuracy estimates obtained from case-control studies including well-defined groups of subjects with or without disease may not be applicable to the clinically relevant population.

Adult↗
PubMed2003

Making image guidance work: understanding control of accuracy.

Use of image-guided surgery is becoming increasingly common in both sinus surgery and neuro-otologic applications. The purpose of this study was to determine the effect of fiducial distribution and mean fiducial error on point accuracy. Using a plastic model, we determined that optimal navigation accuracy was achieved by surrounding the operative target with a widespread field of fiducials. True accuracy was always highest when we targeted a surface point. Accuracy was decreased at points removed from the center of the registration target zone created by the fiducials. Inaccurate registration resulted in increased mean fiducial error and lower accuracy at the target point. Understanding the registration process will enhance the utility of image-guided surgery in otolaryngology and skull base surgery.

Cranial Fossa, Middle↗
PubMed1988

The accuracy of blood glucose testing by children.

While studies have evaluated the accuracy of adult patients and health personnel in reading various glucose oxidase impregnated strips to estimate blood glucose, there are no studies exclusively evaluating the accuracy of children with diabetes reading their own strips as compared to a staff member, and meter to meter variability in reading these strips. We evaluated the accuracy of reading chemstrip bG by children at a summer camp. The children's visual readings of their own strips were compared to the visual reading of a single staff member. A total of 356 Chemstrip bG's were visually read by diabetic children and a single trained staff member at a summer camp for diabetics. The strips were then analyzed by two Accu-Chek bG meters. Intermachine variability was found to be negligible over the entire bG range. For the purposes of this study, we define accurate visual readings as those within +/- 15 percent of the meter reading of a given strip. At low bG values (40-79 mg/dl), accuracy by children and staff is low, with underestimating occurring in 39 percent of staff readings and 57 percent of children's readings. At intermediate bG values (120-239 mg/dl) readings are more accurate, especially when read by the staff, with misreadings occurring in only 16-19 percent of the strips. At high bG values (240-399 mg/dl), accuracy by children is decreased, with underestimation 500 percent more often than staff. We conclude that children are less accurate at reading Chemstrip bG than a trained staff member (51% versus 33% misreading), especially at the upper and lower ranges of bG values when visual readings are least accurate, and the need for therapeutic intervention is the greatest.

Adolescent↗
PubMedDate not supplied

A comparison of user accuracy, techniques, and learning time of various systems for self blood glucose monitoring.

Accuracy of results of self blood glucose monitoring (SBGM) has been shown to be technique and user dependent. Thirty patients, using four commercially available meters (Accu-Chek II, Glucometer II, Glucoscan 2000, and ExacTech), were studied to test the relative accuracy, technique error rates, and learning time for the four meters. No significant difference was found in user accuracy among the four meters. The mean number of technique errors was significantly smaller with the ExacTech system compared with the other three. No significant changes in user accuracy were seen after 1 week of practice with unfamiliar meters. The authors conclude that while all meters had approximately the same user accuracy, the ExacTech meter, which required the least user technique, had fewer user errors and required less time to learn to use.

Adult↗
PubMedDate not supplied

Estimating diagnostic test accuracy using a "fuzzy gold standard".

This study uses Monte Carlo methods to analyze the consequences of having a criterion standard ("gold standard") that contains some error when analyzing the accuracy of a diagnostic test using ROC curves. Two phenomena emerge: 1) When diagnostic test errors are statistically independent from inaccurate ("fuzzy") gold standard (FGS) errors, estimated test accuracy declines. 2) When the test and the FGS have statistically dependent errors, test accuracy can become overstated. Two methods are proposed to eliminate the first of these errors, exploring the risk of exacerbating the second. Both require a probabilistic (rather than binary) gold-standard statement (e.g., probability that each case is abnormal). The more promising of these, the "two-truth" method, selectively eliminates those cases where the gold standard is most ambiguous (probability near 0.5). When diagnostic test and FGS errors are independent, this approach can eliminate much of the downward bias caused by FGS error, without meaningful risk of overstating test accuracy. When the test and FGS have dependent errors, the resultant upward bias can cause test accuracy to be overstated, in the most extreme cases, even before the offsetting "two-truth" approach is employed.

Clinical Laboratory Techniques↗
PubMed1999

Accuracy of circadian entrainment under fluctuating light conditions: contributions of phase and period responses.

The accuracy with which a circadian pacemaker can entrain to an environmental 24-h zeitgeber signal depends on (a) characteristics of the entraining signal and (b) response characteristics and intrinsic stability of the pacemaker itself. Position of the sun, weather conditions, shades, and behavioral variations (eye closure, burrowing) all modulate the light signal reaching the pacemaker. A simple model of a circadian pacemaker allows researchers to explore the impact of these factors on pacemaker accuracy. Accuracy is operationally defined as the reciprocal value of the day-to-day standard deviation of the clock times at which a reference phase (0) is reached. For the purpose of this exploration, the authors used a model pacemaker characterized solely by its momentary phase and momentary velocity. The average velocity determines the time needed to complete one pacemaker cycle and, therefore, is inversely proportional to pacemaker period. The model pacemaker responds to light by shifting phase and/or changing its velocity. The authors assumed further that phase and velocity show small random fluctuations and that the velocity is subject to aftereffects. Aftereffects were incorporated mathematically in a term allowing period to contract exponentially to a stable steady-state value, with a time constant of 69 d in the absence of light. The simulations demonstrate that a pacemaker reaches highest accuracy when it responds to light by simultaneous phase shifts and changes of its velocity. Phase delays need to coincide with slowing down and advances with speeding up; otherwise, no synchronization to the zeitgeber occurs. At maximal accuracy, the changes in velocity are such that the average period of the pacemaker under entrained conditions equals 24 h. The results suggest that during entrainment, the pacemaker adjusts its period to 24 h, after which daily phase shifts to compensate for differences between the periods of the zeitgeber and the clock are no longer necessary. On average, phase shifts compensate for maladjustments of phase and velocity changes compensate for maladjustments of period.

Animals↗
PubMed1999

Impact of an instructional program on nurses' accuracy in capillary blood glucose monitoring.

This experiment examined the accuracy of capillary blood glucose monitoring using the visual glucose oxidase strip (Chemstrip) procedure. Also, the effects of a certification program for nurses on the accuracy of glucose oxidase strip monitoring by registered nurses were analyzed. Seventy nurses and 123 patients participated. Data were collected from nurses' recordings of visual Chemstrip procedure results and from the concurrent laboratory blood glucose determinations for 3 months. The data included 70 Chemstrip recordings and 70 concurrent laboratory blood glucose recordings in the experimental group and 68 Chemstrip and 68 concurrent laboratory glucose recordings in the control group. Data analysis revealed that the accuracy of the nurses' performance of the glucose oxidase strip procedure was inadequate. A certification program did, however, dramatically improve the accuracy of the procedure. Proximity of time between the certification program and the performance of the glucose oxidase strip procedure did not affect accuracy.

Blood Glucose↗
PubMed2002

Accuracy of MMPI-A scales ACK, MAC-R, and PRO in detecting comorbid substance abuse among psychiatric inpatients.

This study investigated the accuracy of various indices involving the MMPI-A scales, ACK, MAC-R, and PRO in diagnosing substance abuse in a sample of 79 psychiatric inpatients. In the full sample, 89.9% of the cases were accurately classified by at least one of the three scales. The overall accuracy of classification was similar among males, females, Caucasians, and African Americans, although there was a tendency for more false positive misclassifications among males. Profile code type moderated the accuracy of classification with greatest accuracy for code types including Scales 1, 2, 3, 5, or 0 and least accuracy for code types including Scales 4, 6, or 9. ACK, MAC-R, and PRO were better at screening out cases of substance abuse than in accurately identifying those adolescents who were using substances.

Adolescent↗
PubMed2006

Does ADHD in adults affect the relative accuracy of metamemory judgments?

OBJECTIVE: Prior research suggests that individuals with ADHD overestimate their performance across domains despite performing more poorly in these domains. The authors introduce measures of accuracy from the larger realm of judgment and decision making--namely, relative accuracy and calibration--to the study of self-evaluative judgment accuracy in adults with ADHD. METHOD: Twenty-eight adults with ADHD and 28 matched controls participate in a computer-administered paired-associate learning task and predict their future recall using immediate and delayed judgments of learning (JOLs). Retrospective confidence judgments are also collected. RESULTS: Groups perform equally in terms of judgment magnitude and absolute judgment accuracy as measured by discrepancy scores and calibration curves. Both groups benefit equally from making their JOL at a delay, and the group with ADHD show higher relative accuracy for delayed judgments. CONCLUSION: Results suggest that under certain circumstances, adults with ADHD can make accurate judgments about their future memory.

Adolescent↗
PubMed2004

Recalling sexual partners: the accuracy of self-reports.

Accuracy of recall of the number of sexual partners individuals had over a period of one month, three months, six months and one year was studied in a group of 285 young, single, heterosexual adults. Self-reports of the number of partners were obtained on a weekly basis and then compared with recall of behavior over longer time periods that overlapped the weekly measures. For individuals who claimed abstinence or who claimed to be monogamous, accuracy of recall was relatively high, especially at the shorter time frames. Level of education was related to accuracy for claimed abstainers, such that lower levels of education were associated with lower accuracy of recall. Accuracy rates for individuals who reported having multiple sexual partners tended to be lower and were found to be related to one's propensity to engage in casual sex.

Adult↗
PubMed2005

Accuracy of frameless and frame-based image-guided stereotactic brain biopsy in the diagnosis of glioma: comparison of biopsy and open resection specimen.

OBJECTIVES: Tissue heterogeneity and rapid tumor progression may decrease the accuracy a prognostic value of stereotactic brain biopsy in the diagnosis of gliomas. Correct tumor grading is therefore dependent on the accuracy of biopsy needle placement. There has been a dramatic increase in the utilization of frameless image-guided stereotactic brain biopsy; however, its accuracy in the diagnosis of glioma remains unstudied. METHODS: The diagnoses of 21 astrocytic brain tumors were derived using image-guided stereotactic biopsy (12 frame-based, nine frameless) and followed by open resection of the lesion 1.5 (0.5-4) months later. The histologic diagnoses yielded by the biopsy were compared with subsequent histologic diagnosis from open tumor resection. RESULTS: Histology of 21 stereotactic biopsies accurately represented the greater lesion at open resection a median of 45 days later in 16 (76%) cases and correctly guided therapy in 19 (91%) cases. Biopsy accuracy of frameless versus frame-based stereotaxis was similar (89 versus 66%, p=0.21). In three (14%) cases, biopsy specimens were adequate to diagnose glioma; however, histology was insufficient for definitive tumor grading. Anaplastic oligodendroglioma (ODG) was under-graded as low-grade ODG in one (5%) case. Biopsy of new onset glioblastoma multiforme (GBM) yielded necrosis/gliosis and was termed non-diagnostic in one patient. Tumors <50 cm(3) were 8-fold less likely to accurately represent the grade of the entire lesion at resection compared with lesions <50 cm(3) (OR, 8.8; 95% CI, 0.9-100, p=0.05). DISCUSSION: Both frameless and frame-based MRI-guided stereotactic brain biopsy are safe and accurately represent the larger glioma mass sufficiently to guide subsequent therapy. Large tumor volume had a higher incidence of non-concordance. Increasing the number of specimens taken through the long dimension of large tumors may improve diagnostic accuracy.

Adult↗
PubMed1998

Assessment of accuracy and applicability of a new electronic peak flow meter and asthma monitor.

The aim of this study was to assess the accuracy and applicability of a portable electronic peak flow meter combined with an asthma monitor (AM1, Jaeger, Germany) which measures peak expiratory flow (PEF), forced expiratory volume in one second (FEV1) and forced vital capacity (FVC). The technical accuracy in PEF, FEV1 and FVC measurement was tested according to American Thoracic Society (ATS) criteria for monitoring devices using a flow generator. In addition, the effect of connecting a heated screen pneumotachograph (PT) to the AM1 was determined and the accuracy in FEV1 determinations was evaluated by simultaneous measurements in 49 normal volunteers. The devices tested fulfilled all ATS criteria for monitoring devices with respect to the accuracy of PEF, FEV1, and FVC measurements. The conditions of intra- and interdevice variability were satisfied in all cases. Compared with the PT, the AM1 showed about 4% lower values in FEV1, as measured in the 49 subjects. In conclusion, the electronic peak flow meter and asthma monitor AM1 yielded valid measurements of peak expiratory flow and forced expiratory volume in one second, which matched the accuracy criteria of the American Thoracic Society standards for monitoring devices.

Adult↗