Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Accuracy”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 955 records · Page 53Linked to original sources
PubMed1984

[Diagnostic accuracy of sonography in liver metastases, with special reference to the primary tumor].

The accuracy of ultrasonography in the detection of liver metastases was studied in 245 patients. Sensitivity, specificity and positive and negative accuracy were defined and calculated. Taking into account only metastases more than 15 mm in diameter, sensitivity was 75.5%, positive accuracy was even higher at 83.0%. Specificity and negative accuracy were above 90%. The results are largely dependent on the type of primary tumour. Sensitivity for metastases of a bronchial or gastric carcinoma was about 50%. The results indicate that a positive ultrasound finding generally need not be checked by other methods, while a negative result, especially in certain types of tumour, is by no means sufficient to exclude metastases.

Breast Neoplasms↗
PubMed2005

Numerical study of the accuracy and efficiency of various approaches for Monte Carlo surface hopping calculations.

A one-dimensional, two-state model problem with two well-separated avoided crossing points is employed to test the efficiency and accuracy of a semiclassical surface hopping technique. The use of a one-dimensional model allows for the accurate numerical evaluation of both fully quantum-mechanical and semiclassical transition probabilities. The calculations demonstrate that the surface hopping procedure employed accounts for the interference between different hopping trajectories very well and provides highly accurate transition probabilities. It is, in general, not computationally feasible to completely sum over all hopping trajectories in the semiclassical calculations for multidimensional problems. In this case, a Monte Carlo procedure for selecting important trajectories can be employed. However, the cancellation due to the different phases associated with different trajectories limits the accuracy and efficiency of the Monte Carlo procedure. Various approaches for improving the accuracy and efficiency of Monte Carlo surface hopping procedures are investigated. These methods are found to significantly reduce the statistical sampling errors in the calculations, thereby increasing the accuracy of the transition probabilities obtained with a fixed number of trajectories sampled.

Journal Article↗
PubMed2006

High-accuracy extrapolated ab initio thermochemistry. II. Minor improvements to the protocol and a vital simplification.

The recently developed high-accuracy extrapolated ab initio thermochemistry method for theoretical thermochemistry, which is intimately related to other high-precision protocols such as the Weizmann-3 and focal-point approaches, is revisited. Some minor improvements in theoretical rigor are introduced which do not lead to any significant additional computational overhead, but are shown to have a negligible overall effect on the accuracy. In addition, the method is extended to completely treat electron correlation effects up to pentuple excitations. The use of an approximate treatment of quadruple and pentuple excitations is suggested; the former as a pragmatic approximation for standard cases and the latter when extremely high accuracy is required. For a test suite of molecules that have rather precisely known enthalpies of formation {as taken from the active thermochemical tables of Ruscic and co-workers [Lecture Notes in Computer Science, edited by M. Parashar (Springer, Berlin, 2002), Vol. 2536, pp. 25-38; J. Phys. Chem. A 108, 9979 (2004)]}, the largest deviations between theory and experiment are 0.52, -0.70, and 0.51 kJ mol(-1) for the latter three methods, respectively. Some perspective is provided on this level of accuracy, and sources of remaining systematic deficiencies in the approaches are discussed.

Journal Article↗
PubMedDate not supplied

Assessment of left ventricular ejection fraction with quantitative gated SPECT: accuracy and correlation with first-pass radionuclide angiography.

BACKGROUND: Quantitative gated single photon emission computed tomography (SPECT [QGS]) software is widely used for the assessment of left ventricular ejection fraction (LVEF). Potentially confounding variables that may affect the accuracy of quantitative analysis of LVEF remain undefined. This study evaluated the accuracy of QGS as a means of determining LVEF in a wide range of LVEF values; evaluated the effect of extracardiac activity, count statistics, heart size, and perfusion defects on the accuracy of QGS LVEF; and compared QGS LVEF obtained at rest with that obtained after stress. METHODS AND RESULTS: QGS-derived LVEF was compared with rest first-pass radionuclide angiography (FPRNA) LVEF in 400 electrocardiographic-gated SPECT studies. The overall correlation between QGS and FPRNA LVEF was only fair (r = 0.66, SEE = 11.85%). In 35 of the patient studies (9%) with high extracardiac activity, the automated software failed, and no correlation was obtained. In the remaining 365 patient studies (91%), left ventricular contours were successfully identified. In these studies, correlation was better (r = 0.74, SEE = 9.77%). Agreement was better for images with high counts (r = 0.81, SEE = 8.66%) than for images with low counts (r = 0.61, SEE = 11.17%). Patient studies with abnormal LVEF had better correlation (r = 0.77, SEE = 6.4%) than studies with normal LVEF (r = 0.46, SEE = 10.2%). Agreement between QGS LVEF and FPRNA LVEF was better in hearts with large end diastolic volumes (>104 mL) than in hearts with small volumes. Overall, mean QGS LVEF was lower than mean FPRNA LVEF (54%+/-14% vs. 58%+/-14%, P<.0001). There was no difference between mean rest and stress QGS LVEF in the same patients, even in patients with stress-induced ischemia. CONCLUSIONS: QGS is a valuable method for assessing resting LVEF. However, QGS LVEF is often lower than FPRNA LVEF. Accuracy is affected by high extracardiac activity, low count density, and small size of the left ventricle.

Adult↗
PubMedDate not supplied

Attenuation correction and gating synergistically improve the diagnostic accuracy of myocardial perfusion SPECT.

BACKGROUND: The diagnostic accuracy of myocardial perfusion single photon emission computed tomography is limited by soft tissue attenuation. Artifacts may be reduced by attenuation correction (AC) or compensated for by assessment of wall motion in gated images. We studied the benefit of gating and AC, both separately and combined, in improving accuracy. METHODS AND RESULTS: Sixty-six subjects (27 with > or =50% angiographic stenosis, 5 with <50% stenosis, and 34 Bayesian normal volunteers) underwent gated AC single photon emission computed tomography. Images were reconstructed and independently viewed in 4 ways: static with motion correction (MC) only, gated with MC only, static with MC plus blur correction plus AC (referred to as combined corrections [CC]), and gated with CC. Images were interpreted by 2 blinded observers for overall presence of coronary disease and for vascular territory (left anterior descending [LAD], left circumflex [LCx], and right coronary artery [RCA]). Statistical analysis of sensitivity and normalcy was done by means of the Cochran Q test. Overall diagnostic accuracy showed statistically significant improvement (P =.05 for sensitivity, P <.001 for normalcy), progressing from static MC to gated MC to static CC to gated CC (sensitivity/normalcy = 85%/54%, 78%/62%, 93%/77%, and 96%/85%, respectively, for the 4 reconstruction and viewing approaches). Sensitivity was highest in all 3 vascular territories for the combination of gating and CC; normalcy was also highest with the same combination for the LAD and RCA territories; sensitivity/normalcy with this combination was 85%/87% for the LAD, 69%/87% for the LCx, and 89%/87% for the RCA territory. CONCLUSIONS: The combination of gating and CC provides the highest diagnostic accuracy, and gating and AC should thus be considered complementary and synergistic.

Artifacts↗
PubMed2000

Accuracy of computerized automatic identification of cephalometric landmarks.

Computerized cephalometric analysis can include both landmark identification and determination of linear or angular measurements. Although its use is time saving compared with a manual method, the accuracy of automatic landmark identification remains unclear. The purpose of this study was to evaluate the accuracy of a computerized automatic landmark identification system that used an edge-based technique. The technique divides the scanned cephalogram into 8 rectangular subimage regions. After the resolution of these subimages is reduced, the edges are detected and the landmarks are located automatically. Thirteen landmarks were selected for assessment on a set of 10 test cephalograms. The results showed that the errors between manual and computerized identification for landmarks were not significantly different (P > .05) for 5 of 13 landmarks: sella, nasion, porion, orbitale, and gnathion. These results suggest that the accuracy of computerized automatic identification is acceptable for certain landmarks only. Further studies to improve the accuracy of computerized automated landmark identification are needed.

Cephalometry↗
PubMed2001

Accuracy of mandibular cross-sectional imaging with tuned- aperture computed tomography (TACT), iteratively reconstructed TACT, and multidirectional, linear, and transverse panoramic tomography.

OBJECTIVE: This study was designed to compare 5 modalities with respect to accuracy in mandibular cross-sectional imaging. The modalities tested were tuned-aperture computed tomography (TACT), iteratively reconstructed TACT, multidirectional tomography, linear tomography, and transverse panoramic tomography. STUDY DESIGN: Twenty sites were selected from 3 dry human mandibles, and cross-sectional views were imaged through use of each of the 5 modalities. A quantitative analysis included measurements of 2 linear distances; a qualitative study included image evaluation by 6 observers. A nested mixed analysis of variance model was used to control for mandibles and locations within mandibles for the quantitative analysis; the Cochran-Mantel-Haenszel test was used for the qualitative analysis. RESULTS: There was a significant difference in measurement error for maximum height but not for width. There was also a significant difference in qualitative image evaluation results. CONCLUSIONS: Of the 5 modalities tested, the narrow-layer multidirectional tomographic technique produced the greatest diagnostic accuracy and quality in cross-sectional imaging. The transverse panoramic tomographic technique produced the least diagnostic accuracy and quality. Linear tomography, TACT, and iteratively reconstructed TACT were intermediate in accuracy and quality.

Analysis of Variance↗
PubMed2003

Evaluation of the accuracy of three techniques used for multiple implant abutment impressions.

STATEMENT OF PROBLEM: Movement of pick-up type impression copings inside the impression material during clinical and laboratory phases may cause inaccuracy in transferring the spatial position of implants from the oral cavity to the master cast. As a consequence, the laboratory technician may fabricate a restoration that requires corrective procedures. PURPOSE: This in vitro study evaluated the accuracy of 3 different impression techniques using polyether impression material to obtain a master cast for the fabrication of a prosthesis that would fit passively on multiple implants. MATERIAL AND METHODS: A machined metal model with 6 implants and abutments and a corresponding, passively fitting, matching metal template were fabricated. A total of 45 medium-consistency polyether impressions (Impregum Penta) of this model were made with pick-up type square impression copings. Three groups of 15 each were made with different impression techniques: in group 1, nonmodified square impression copings were used; in group 2, square impression copings were used and joined together with autopolymerizing acrylic resin before the impression procedure; and in group 3, square impression copings previously airborne particle-abraded and coated with the manufacturer-recommended impression adhesive were used. The matching metal template, which had been passively fit to the metal model so that it encountered no visually perceptible resistance or rocking on the abutments, was used as the control for evaluation of the accuracy of passive fit. A single calibrated and blinded examiner visually evaluated each cast. Positional accuracy of the abutments was numerically assessed with an optical scanner at original magnification x 10, which provided measurements to within 2 microm of the variations of the casts with respect to the horizontal distances between the 2 most posterior abutments and the 2 most anterior abutments. Data were analyzed with a 1-way analysis of variance at alpha=.05, followed by the Student Newman-Keuls method (P=.05). RESULTS: Visual examination of the casts from group 1 revealed discrepancies between 1 or more abutments and the metal template. Visual analysis of the master casts from groups 2 and 3 revealed close alignment of the metal template on all 6 abutments. One-way analysis of variance analyzed the numerical data obtained with the optical scanner and revealed significant differences among the 3 impression techniques (P<.001). The Newman-Keuls procedure disclosed significant differences between the groups, with group 2 and 3 casts being significantly more accurate than group 1 casts (P=.05). The distance between abutments 1 and 6 compared to the standard metal model was 33.83 microm (SD +/- 5.4) greater on group 2 casts, 31.72 microm (SD +/- 4.6) greater on group 3 casts, and 78.16 microm (SD +/- 22.14) greater on group 1 casts. Distances between the most anterior abutments were also greater than those recorded on the metal model. The distance was 31.42 microm (SD +/- 7.6) greater on group 2 casts, 30.34 microm (SD +/- 6.4) greater on group 3 casts, and 67.91 microm (SD +/- 15.34) greater on group 1 casts. CONCLUSION: Within the limitations of this study, improved accuracy of the master cast was achieved when the impression technique involved square impression copings joined together with autopolymerizing acrylic resin or square impression copings that had been airborne particle-abraded and adhesive-coated.

Air Abrasion, Dental↗
PubMed1998

The effect of pre-movement delays on pointing accuracy in middle childhood.

In adults, the introduction of a pre-response delay has been shown to affect accuracy in pointing tasks while leaving accuracy in perceptual matching tasks unaffected. Here, we report on the effect of pre-movement delays on pointing accuracy in 6-10-year-old children. Children of this age group are of particular interest as their reliance on visual cues to monitor and correct their reaches appears to change during this period of development. Nineteen children were asked to point to the location of a target light after a delay of 0, 1, 2, or 4 s following target extinction. Performance was measured in two conditions: (i) open-loop, where the child reproduced the target locations in complete darkness, and (ii) with visual feedback, where information about hand position was available. Errors in the direction and in the amplitude of each reaching movement were recorded separately. The results show that temporal delay significantly affects the pointing movements of these children. Accuracy (mean) deteriorated after only 1 s whereas the precision (standard deviation) of the responses deteriorated after 4 s. Errors in amplitude, but not errors in direction, were reduced by the provision of visual feedback. Taken together, the findings suggest that amplitude and directional components of pointing in childhood utilise different sources of information, which differ in the extent to which temporal constraints operate.

Child↗
PubMed2003

Timing accuracy in motion extrapolation: reverse effects of target size and visible extent of motion at low and high speeds.

By varying target size, speed, and extent of visible motion we examined the timing accuracy in motion extrapolation. Small or large targets (0.2 or 0.8 deg) moved at either 2.5, 5, or 10 deg s(-1) across a horizontal path (2.5 or 10 deg) and then vanished behind an occluder. Observers responded when they judged that the target had reached a randomly specified position between 0 and 12 deg. With higher speeds, the timing accuracy (the reverse of absolute error) was better for small than for large targets, and for long than for short visible extents. With low speed, these effects were reversed. In addition, while long visible extents yielded a greater accuracy at high than at low speeds, for short extents the accuracy was much better with the low speed. The findings suggest that, when extrapolating motion with targets and visible extents of different sizes, the visual system implements different scaling algorithms depending on target speed. At higher speeds, processing of visible and occluded motion is likely to share a common scaling mechanism based on velocity transposition. Reverse effects for target size and extent of visible motion at low and high speeds converge with the assumption of two distinct speed-tuned motion-processing mechanisms in human vision.

Humans↗
PubMed1985

Speed-accuracy characteristics of saccadic eye movements.

Speed-accuracy trade-off characteristic of horizontal saccadic eye movements were examined in this study. Unlike limb movements, saccadic eye movements are preprogrammed, unidimensional, and do not involve target impact. Hence, they provide an optimal test of the impulse variability account of the speed-accuracy trade-off in rapid movements. Subjects were required to alternately look at two target lights as fast and as accurately as possible for a period of 10 s. Target lights subtended angles of 5, 10, 15, and 20 degrees. By restricting target distances to less than 20 degrees of arc, the speed-accuracy relation was examined for single horizontal saccadic movements of the eye. movement of the dominant eye was tracked with an infra-red eye monitoring device. Fifty saccadic movements of the eye were recorded for each target distance and used to compute the average amplitude, duration, and velocity of eye movements, as well as, movement endpoint variability. An increase in both average velocity and movement endpoint variability with increasing movement amplitude was found. This, together with the unique features of the eye movement system, support the impulse variability account of the speed-accuracy trade-off in rapid movements.

Journal Article↗
PubMed2005

Cognitive appraisal accuracy moderates the relationship between injury severity and psychosocial outcomes in traumatic brain injury.

OBJECTIVE: Traumatic brain injury (TBI) frequently results in significant changes in physical, cognitive and emotional status. Outcomes after TBI may be related to accurate appraisal of these changes. This study examined the relationship between cognitive appraisal accuracy and psychosocial outcomes in TBI survivors. METHODS: Participants were male and female TBI survivors (n=103) who were at least 6 months post-injury and a family member of each survivor. Appraisal accuracy was assessed using self- and observer-report measures of perceived cognitive difficulties. Family members also completed a measure of psychosocial function. Hierarchical regression techniques were used to determine whether cognitive appraisal accuracy accounted for a significant proportion of variance in psychosocial outcomes. RESULTS: Study findings indicated cognitive appraisal accuracy moderated the relationship between injury severity and aspects of psychosocial function. CONCLUSIONS: The results suggest that brain injury outcomes may be improved when an individual is able to accurately assess limitations.

Adult↗
PubMed2005

Immediate and delayed bilateral transfer of throwing accuracy in male and female children.

In the present study, an attempt was made to examine the nature and persistence of bilateral transfer of a throwing skill for a large sample of male and female children. One hundred sixty children ages 6, 8, 10, and 12 years were randomly assigned to either an experimental or control group with an equal number of boys and girls in each group. The experiment lasted 2 days and consisted of a pretest, a practice phase, an immediate transfer test, and a delayed transfer test. On the pretest, each participant performed 10 trials of a novel one-hand throwing task. Following the pretest, participants in the experimental group practiced the skill with the hand opposite the one used during the pretest until they had successfully reached a designated criterion for their age. Participants in the control group performed a balancing activity. Following the practice phase, all participants performed immediate (10 min later) and delayed (24 hr later) transfer tests under the same conditions as the pretest. The results revealed no group differences on the pretest but significantly higher throwing accuracy for the experimental group than the control group on both transfer tests. In addition, boys' throwing accuracy was significantly superior to the girls. It was concluded that bilateral transfer of throwing accuracy can be both a temporary and relatively persistent phenomenon for children and the superior throwing accuracy for boys is consistent with similar gender differences in throwing distance and throwing velocity (Thomas & French, 1985).

Analysis of Variance↗
PubMed1999

Accuracy of ultrasonography and magnetic resonance imaging in detecting failure of breast implants filled with silicone gel.

We prospectively studied the accuracy of magnetic resonance imaging (MRI) and ultrasonography (US) for preoperative detection of rupture in 35 single-lumen implants filled with silicone gel in 18 patients. The positive predictive value of US for rupture of an implant was 70% and the negative predictive value 64%. Sensitivity and specificity were 44% and 87%, respectively. Accuracy, defined as the total true positive and true negative values divided by the total number of implants studied was 66%. The positive predictive value of MRI was 100% and the negative predictive value 90%. The corresponding sensitivity and specificity were 88% and 100% and the accuracy 94%. MRI offers significantly better diagnostic sensitivity (p = 0.02) and accuracy (p = 0.004), and should be regarded as the "gold standard" in the evaluation of rupture of breast implants filled with silicone gel. When MRI is not readily available, US is an acceptable alternative.

Adult↗
PubMedDate not supplied

Posteroanterior motion test of a lumbar vertebra: accuracy of perception.

PURPOSE: The aim of this study was to investigate the accuracy of perception of forces applied to and displacement produced in an electromechanical one vertebral spinal model, among inexperienced and experienced physical, therapists performing posteroanterior pressure on a lumbar vertebra, before and after a training session. METHODS: Ten relatively inexperienced physical therapists and ten experienced manual therapists participated. An electromechanical single level spinal model was used for applying oscillatory posteroanterior pressure and measuring the forces on and displacement of the vertebra. A digital oscilloscope was used to give direct feedback to the therapists while performing mobilization to discern the magnitude of these two variables. RESULTS: The inexperienced group estimated the displacement accurately but the experienced group was significantly inaccurate (p<0.02), and both groups were inaccurate in estimating the force (p<0.001), before training. Following training, the inexperienced group maintained their accuracy on displacement and the experienced group improved their accuracy significantly (p<0.001). Both groups approached significance in improving their accuracy of force estimation. CONCLUSION: An electromechanical spinal model can be used as training tool along with an oscilloscope. Longer training may be needed for the force than the displacement for accurate perception.

Adult↗
PubMed2000

Practice and feedback effects on the confidence-accuracy relation in eyewitness memory.

It has been claimed that the lack of a reliable confidence-accuracy relation in eyewitness memory stems from eyewitnesses' lack of knowledge concerning their relative expertise. Two studies tested this idea by contrasting the effects of practice alone with practice with feedback in three successive eyewitness tests. Experiment 1 tested recall for events, and Experiment 2 used recognition of faces as test materials. Both studies showed that practice alone did not increase the confidence-accuracy relation, but practice with feedback on relative performance produced robust increases in the confidence-accuracy relation. This suggests that lack of calibration is one factor that causes the reported lack of association between confidence and accuracy for eyewitness memory.

Adolescent↗
PubMed2000

Confidence--accuracy relations for real and suggested events.

Participants completed a multiple item, multiple event version of a traditional misinformation procedure, as well as a battery of individual difference measures. The relation between memory accuracy and self-reported confidence was assessed through the comparison of items involving misinformation and items not involving misinformation. Selected individual differences in the confidence-accuracy relation were also examined for items that did and did not involve false post-event information. Results indicated significant differences between the measure of the confidence-accuracy relationship for misinformation and non-misinformation items. Several significant, although weak, individual difference correlates of the confidence-accuracy relations were also found.

Adolescent↗
PubMed2001

A laboratory evaluation of the accuracy and precision of the photovac snapshot portable gas chromatograph and the Dräger Chip Measurement System monitor for benzene in air measurements.

A laboratory evaluation of the accuracy and precision of two field instruments, the Photovac Snapshot Gas Chromatograph and the Dräger Chip Measurement System (CMS) Monitor, both capable of specific determination of benzene, was carried out. The evaluation was based on the generation of a test atmosphere of known concentration of benzene in a stainless steel calibration chamber and simultaneous sampling of the test atmosphere by each instrument. At the same time, the chamber atmosphere was continuously monitored by one or two data logging photoionization detector (PID) hydrocarbon analysers. A series of six, 10-minute charcoal tube air samples of the test atmosphere was also collected over the 1-hour run and analyzed by gas chromatography. Nine different concentrations ranging from 0.25 ppm to 8 ppm were used. Accuracy was evaluated using National Institute for Occupational Safety and Health (NIOSH) criteria. The Photovac GC consistently met the NIOSH recommended accuracy criteria of +/- 25 percent at or below 1 ppm of benzene, whereas the Drager CMS results generally fell slightly outside this criteria. Compared against less stringent accuracy criteria of +/- 35 percent, all Photovac GC results were acceptable but about 40 percent of Drager CMS results were not. The precision of Photovac GC (CV +/- 10%) is better than Drager CMS (CV = +/- 20% to 40%). Both instruments are, however, good field instruments provided their limitations are taken into account in their use.

Air Pollutants↗