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PubMed2004

Accuracy of continuous nocturnal glucose screening after 48 and 72 hours in type 2 diabetes patients on combined oral and insulin therapy.

OBJECTIVE: To evaluate the accuracy of nocturnal continuous glucose monitoring by CGMS. RESEARCH DESIGN AND METHODS: A CGMS was inserted in 14 type 2 diabetic patients on combined oral and insulin therapy at altogether 15 occasions. During the second (48 hours) and third (72 hours) night of registration each subject was observed and plasma glucose was analysed seven times during the night by venous sampling and compared to CGMS. These venous values were not used for calibration of the sensor. Pairs of data were analysed using correlation coefficient, Bland-Altman graphs and Clarke Error Grid analysis. RESULTS: 32% of CGMS data did not meet the quality criteria for optimal accuracy and were excluded. A correlation coefficient of 0.80 (p < 0.0001) was seen after 48 hours and a lower coefficient of 0.33 (p = 0.0082) after 72 hours. Bland-Altman analyses demonstrated that the dispersion of the values around the mean of differences was wider after 72 hours as compared to after 48 hours. In the Clark Error Grid analysis 100% of data were within zones A and B after 48 hours, with 60% in zone A. After 72 hours only 44% were in zone A and 7% of data were in the clinically unacceptable zone D. CONCLUSION: The MiniMed Medtronic CGMS has acceptable nocturnal accuracy after 48 hours of registration, but the accuracy thereafter deteriorates with time, implicating that the CGMS thereafter may prove less useful for nocturnal monitoring.

Administration, Oral↗
PubMed1997

All in one: a highly detailed rotamer library improves both accuracy and speed in the modelling of sidechains by dead-end elimination.

BACKGROUND: About a decade ago, the concept of rotamer libraries was introduced to model sidechains given known mainchain coordinates. Since then, several groups have developed methods to handle the challenging combinatorial problem that is faced when searching rotamer libraries. To avoid a combinatorial explosion, the dead-end elimination method detects and eliminates rotamers that cannot be members of the global minimum energy conformation (GMEC). Several groups have applied and further developed this method in the fields of homology modelling and protein design. RESULTS: This work addresses at the same time increased prediction accuracy and calculation speed improvements. The proposed enhancements allow the elimination of more than one-third of the possible rotameric states before applying the dead-end elimination method. This is achieved by using a highly detailed rotamer library allowing the safe application of an energy-based rejection criterion without risking the elimination of a GMEC rotamer. As a result, we gain both in modelling accuracy and in computational speed. Being completely automated, the current implementation of the dead-end elimination prediction of protein sidechains can be applied to the modelling of sidechains of proteins of any size on the high-end computer systems currently used in molecular modelling. The improved accuracy is highlighted in a comparative study on a collection of proteins of varying size for which score results have previously been published by multiple groups. Furthermore, we propose a new validation method for the scoring of the modelled structure versus the experimental data based upon the volume overlap of the predicted and observed sidechains. This overlap criterion is discussed in relation to the classic RMSD and the frequently used +/- 40 degrees window in comparing chi 1 and chi 2 angles. CONCLUSIONS: We have shown that a very detailed library allows the introduction of a safe energy threshold rejection criterion, thereby increasing both the execution speed and the accuracy of the modelling program. We speculate that the current method will allow the sidechain prediction of medium-sized proteins and complex protein interfaces involving up to 150 residues on low-end desktop computers.

Algorithms↗
PubMed2000

Oculomotor impairment after 1 night of total sleep deprivation: a dissociation between measures of speed and accuracy.

OBJECTIVES: The present study examined the effects of 40 h of sleep deprivation and of time-of-day on saccadic and smooth pursuit oculomotor performance. METHODS: Nine normal subjects slept for 3 consecutive nights in the laboratory (one adaptation, one baseline, one recovery). Baseline and recovery were separated by a period of 40 h of continuous wakefulness, during which subjects were tested every 2 h. Oculomotor performance assessed at the following hours: 10:00, 12:00, 14:00, 16:00, 18:00, 20:00, 22:00, of both the days preceding and following the sleep deprivation night, as well as at 24:00, 02:00, 04:00, 06:00 and 08:00 h during the deprivation period. RESULTS: Saccade latency increased and peak velocity decreased significantly during the post-deprivation day; saccadic accuracy was unaffected. As regards smooth pursuit performance, phase (a measure of accuracy) was not affected by sleep loss, while velocity gain significantly decreased during the day that followed the sleep deprivation night. Significant time-of-day effects on the considered oculomotor variables except saccadic accuracy were also found, indicating an overall performance impairment during the night. CONCLUSIONS: It is concluded that 40 h of sleep deprivation significantly impaired diurnal performance in pursuit and saccadic tasks. This performance worsening is limited to the measures of speed, while accuracy is not affected by sleep loss. A significant operational relevance of these results is suggested, since saccadic velocity has recently been found to be negatively correlated with simulator vehicle crash rates.

Adult↗
PubMed2002

A valid and reliable method for measuring the kicking accuracy of soccer players.

Kicking accuracy is an important component of soccer performance. We constructed a plywood target measuring 243.5cm wide x 122cm high. Carbon paper applied to the surface of the target allowed measurement by 2 raters from a bull's-eye to 10 ball marks left by kicks. Intraclass correlation coefficients with 95% confidence intervals were used to determine the intra- and interrater reliability of the measurement to each ball mark. Mean and median distances from bulls-eye to ball mark were 89.9cm and 97.9cm, respectively (range, 25.7 to 150.75cm). The intraclass correlation coefficients for intra- and interrater reliability were 0.99. The root mean square error of measurement indicated that accuracy of measurement was within 0.15cm. These results suggest that our method of assessing kicking accuracy is a valid and reliable tool for analysing performance. Because this tool closely replicates kicking into a soccer goal, we feel that it also has validity. To our knowledge, no other tool or measure (e.g.. number of shots on goal or number of goals per game) has comparable validity and reliability. This method can be used as a training tool and for future investigations of kicking accuracy.

Confidence Intervals↗
PubMed2003

Diagnostic accuracy of nucleic acid amplification tests for tuberculous meningitis: a systematic review and meta-analysis.

Conventional tests are not always helpful in making a diagnosis of tuberculous meningitis. We did a systematic review and meta-analysis to establish the summary accuracy of nucleic acid amplification (NAA) tests for tuberculous meningitis. We searched six electronic databases and contacted authors, experts, and manufacturers. Measures of diagnostic accuracy were pooled using a random effects model. 49 studies met our inclusion criteria. The summary estimates in 14 studies with commercial NAA tests were: sensitivity 0.56 (95% CI 0.46, 0.66), specificity 0.98 (0.97, 0.99), positive likelihood ratio 35.1 (19.0, 64.6), negative likelihood ratio 0.44 (0.33, 0.60), and diagnostic odds ratio 96.4 (42.8, 217.3). In the 35 studies with in-house ("home-brew") tests, the summary accuracy could not be established with confidence because of wide variability in test accuracy. On current evidence, commercial NAA tests show a potential role in confirming tuberculous meningitis diagnosis, although their overall low sensitivity precludes the use of these tests to rule out tuberculous meningitis with certainty.

Humans↗
PubMedDate not supplied

Accuracy of fourth-graders' dietary recalls of school breakfast and school lunch validated with observations: in-person versus telephone interviews.

OBJECTIVE: To investigate the accuracy of children's dietary recalls of school breakfast and school lunch validated with observations and obtained during in-person versus telephone interviews. DESIGN: Each child was observed eating school breakfast and school lunch and was interviewed that evening about that day's intake. SETTING: Ten elementary schools. PARTICIPANTS: A sample of fourth-graders was randomly selected within race (black, white) and gender strata, observed, and interviewed in person (n = 33) or by telephone (n = 36). MAIN OUTCOMES MEASURED: Rates for omissions (items observed but not reported) and intrusions (items reported but not observed) were calculated to determine accuracy for reporting items. A measure of total inaccuracy was calculated to determine inaccuracy for reporting items and amounts combined. ANALYSIS: Analysis of variance; chi-square. RESULTS: Interview type (in person, telephone) did not significantly affect recall accuracy. For omission rate, intrusion rate, and total inaccuracy, means were 34%, 19%, and 4.6 servings for in-person recalls and 32%, 16%, and 4.3 servings for telephone recalls of school breakfast and school lunch. CONCLUSIONS AND IMPLICATIONS: The accuracy of children's recalls of school breakfast and school lunch is not significantly different whether obtained in person or by telephone. Whether interviewed in person or by telephone, children reported only 67% of items observed; furthermore, 17% of items reported were not observed.

Child↗
PubMed2005

Prospective evaluation of the accuracy of the intraductal secretin stimulation test in the diagnosis of chronic pancreatitis.

BACKGROUND & AIMS: The standard secretin stimulation test (SST) is the accepted gold standard for pancreatic function testing. The intraductal secretin stimulation test (IDST) performed at the time of endoscopic retrograde cholangiopancreatography (ERCP) has been proposed as a more feasible way to evaluate pancreatic function. The accuracy of the IDST for the diagnosis of chronic pancreatitis (CP) has not been well defined. METHODS: We prospectively evaluated patients with suspected CP. The IDST, SST, and ERCP were performed in each of the 19 study patients. The SST and ERCP were used as independent diagnostic standards against which the results of the IDST were compared directly to determine the sensitivity, specificity, and accuracy of the IDST. RESULTS: When the SST was used as a diagnostic standard for CP, the sensitivity of the IDST was 80% (95% confidence interval [CI], 44%-97%), the specificity was 22% (95% CI, 2%-60%), and the overall accuracy was 52% (95% CI, 28%-75%). The positive predictive value was 53% and the negative predictive value was 50%. When the pancreatogram was used as the diagnostic standard, the sensitivity of the IDST was 100% (95% CI, 69%-100%), the specificity was 55% (95% CI, 21%-86%), and the overall accuracy was 79% (95% CI, 54%-93%). Receiver operator curves showed that there was no optimal cut-off value for peak bicarbonate concentration that led to acceptable sensitivity and specificity. CONCLUSIONS: The IDST is not accurate for the diagnosis of CP.

Adult↗
PubMed2002

Global Positioning System (GPS) location accuracy improvement due to selective availability removal.

Global Positioning System (GPS) is an important new technology for spatio-temporal behaviour studies of animals. Differential correction improves location accuracy. Previously, it mostly removed partially the influence of Selective Availability (SA). SA was deactivated in May 2000. The aim of this study was to quantify the influence of SA cancellation on location accuracy of various GPS receivers. We tested the accuracy of locations obtained from non-differential and differential GPS animal collars before and after SA removal. We found a significant improvement in accuracy for both types of GPS collars. However, differential GPS still provides more accurate locations.

Animal Identification Systems↗
PubMed2006

Mass measurement accuracy in analyses of highly complex mixtures based upon multidimensional recalibration.

Mass spectrometry combined with a range of on-line separation techniques has become a powerful tool for characterization of complex mixtures, including protein digests in proteomics studies. Accurate mass measurements can be compromised due to variations that occur in the course of an on-line separation, e.g., due to excessive space charge in an ion trap, temperature changes, or other sources of instrument "drift". We have developed a multidimensional recalibration approach that utilizes existing information on the likely mixture composition, taking into account variable conditions of mass measurements, and that corrects the mass calibration for sets of individual peaks binned by, for example, the total ion count for the mass spectrum, the individual peak abundance, m/z value, and liquid chromatography separation time. The multidimensional recalibration approach uses a statistical matching of measured masses in such measurements, often exceeding 105, to a significant number of putative known species likely to be present in the mixture (i.e., having known accurate masses), to identify a subset of the detected species that serve as effective calibrants. The recalibration procedure involves optimization of the mass accuracy distribution (histogram), to provide a more confident distinction between true and false identifications. We report the mass accuracy improvement obtained for data acquired using a TOF and several FTICR mass spectrometers. We show that the multidimensional recalibration better compensates for systematic mass measurement errors and also significantly reduces the mass error spread: i.e., both the accuracy and precision of mass measurements are improved. The mass measurement improvement is found to be virtually independent of the initial instrument calibration, allowing, for example, less frequent calibration. We show that this recalibration can provide sub-ppm mass measurement accuracy for measurements of a complex fungal proteome tryptic digest and provide improved confidence or numbers of peptide identifications.

Calibration↗
PubMed1997

Functional wave time-lag focusing matrix-assisted laser desorption/ionization in a linear time-of-flight mass spectrometer: improved mass accuracy.

A strength of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is its ability to analyze mixtures without separation. MALDI mass spectrometers capable of providing a linear mass calibration over a broad mass range should find wide use in these applications. This work addresses issues pertinent to mass measurement accuracy of a time-lag focusing MALDI time-of-flight instrument and presents a new approach to improving mass accuracy by using a functional wave extraction pulse, instead of a square wave, for time-lag focusing. A model is described of an ideal extraction pulse shape that provides constant total kinetic energy for all ions. If total kinetic energy is constant, then there is an exact linear correlation between ion mass and flight time raised to the second power. Using a descending wave extraction pulse, it is demonstrated that mass accuracy of better than 30 ppm using two internal calibrants and better than 70 ppm using external calibrants can be obtained over a 25 ku mass range. The practical aspects of an instrument needed to obtain consistent mass accuracy is discussed. It is found that ion flight time shows a small dependence upon laser flux; flight times increase slightly as the flux increases. But this dependence is much smaller than is observed in continuous-extraction MALDI.

Animals↗
PubMed1998

Fidelity of mutant HIV-1 reverse transcriptases: interaction with the single-stranded template influences the accuracy of DNA synthesis.

We have used random sequence mutagenesis and complementation in a bacterial selection system to establish a large library of immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) mutants with amino acid substitutions in the beta3-beta4 region of the fingers subdomain [Kim, B., Hathaway, T. R., and Loeb, L. A. (1996) J. Biol. Chem. 271, 4872-4878]. We show here that one of these mutants, D76V, exhibits increased accuracy of copying both DNA and RNA templates in a primer extension assay with biased dNTP pools. More detailed analysis of DNA-dependent polymerization showed that the D76V mutation conferred an up to 14-fold increase in fidelity of nucleotide insertion and a 9-fold reduced mutation rate in an M13mp2 lacZalpha forward mutation assay. Substitution at D76 with positively charged (D76R) and nonpolar (D76V and D76I) residues increased replicational accuracy, while substitutions with negatively charged (D76E) and polar residues (D76S and D76C) had little effect on fidelity. We propose that D76 affects replicational accuracy by mediating interaction between the fingers subdomain and the single-stranded template. Our work shows that the Escherichia coli complementation system can yield HIV RT mutants with increased fidelity that have not been isolated from the natural host and that are valuable in understanding the molecular bases of replicational accuracy.

Amino Acid Substitution↗
PubMed2004

SDOCKER: a method utilizing existing X-ray structures to improve docking accuracy.

This paper introduces a new strategy for structure-based drug design that combines high-quality docking with data from existing ligand-protein cocrystal X-ray structures. The main goal of SDOCKER, a new algorithm that implements this strategy, is docking accuracy improvement. In this new paradigm, simulated annealing molecular dynamics is used for conformational sampling and optimization and an additional similarity force is applied on the basis of the positions of ligands from X-ray data that focus the sampling on relevant regions of the active site. Because the structural information from both the ligand and protein active site is included, this approach is more effective in finding the optimal conformation for a ligand-protein complex than the classical docking or similarity overlays. Interestingly, it was found that a 3D similarity-only approach gives comparable docking accuracy to the regular force field approach used in classical docking, given the final structures are minimized in the presence of the protein. The combination of both, as implemented in SDOCKER, is shown here to be more accurate. A significant improvement in docking accuracy has been observed for three different test systems. Specifically an improvement of 10%, 17.5%, and 10% is seen for 37 HIV-1 protease, 32 thrombin, and 23 CDK2 ligands, respectively, compared to docking using the force field alone. In addition, SDOCKER's accuracy performance dependence on the similarity template is discussed. The strategy of utilizing existing ligand X-ray information should prove effective in light of the multitude of structures available from structural genomics approaches.

Algorithms↗
PubMed2000

Witnessing-condition heterogeneity and witnesses' versus investigators' confidence in the accuracy of witnesses' identification decisions.

Undergraduate participants were tested in 144 pairs, with one member of each pair randomly assigned to a "witness" role and the other to an "investigator" role. Each witness viewed a target person on video under good or poor witnessing conditions and was then interviewed by an investigator, who administered a photo line up and rated his or her confidence in the witness. Witnesses also (separately) rated their own confidence. Investigators discriminated between accurate and inaccurate witnesses, but did so less well than witnesses' own confidence ratings and were biased toward accepting witnesses' decisions. Moreover, investigators' confidence made no unique contribution to the prediction of witnesses' accuracy. Witnesses' confidence and accuracy were affected in the same direction by witnessing conditions, and there was a substantial confidence-accuracy correlation when data were collapsed across witnessing conditions. Confidence can be strongly indicative of accuracy when witnessing conditions vary widely, and witnesses' confidence may be a better indicator than investigators'.

British Columbia↗
PubMed2000

Accuracy of bound peptide structures determined by exchange transferred nuclear Overhauser data: a simulation study.

The exchange-transferred NOE method to determine the three-dimensional structure of peptides bound to proteins, or other macromolecular systems, is becoming increasingly important in drug design efforts and for large or multicomponent assemblies, such as membrane receptors, where structural analysis of the full system is intractable. The exchange-transferred nuclear Overhauser effect spectroscopy (etNOESY) method allows the determination of the bound-state conformation of the peptide from the intra-molecular NOE interactions between ligand protons. Because only ligand-ligand NOEs are generally observable, the etNOESY method is restricted to fewer NOEs per residue than direct protein structure determination. In addition, the averaging of relaxation rates between free and bound states affects the measured cross-peak intensities, and possibly the accuracy of distance estimates. Accordingly, the study reported here was conducted to examine the conditions required to define a reliable structure. The program CORONA was used to simulate etNOE data using a rate-matrix including magnetic relaxation and exchange rates for two peptide-protein complexes derived from the reference complex of cAMP-dependent protein kinase ligated with a 24-residue inhibitor peptide. The results indicate that reasonably accurate peptide structures can be determined with relatively few NOE interactions when the interactions occur between non-neighboring residues. The reliability of the structural result is suggested from the pattern of NOE interactions. A structure with an accuracy of approximately 1.3 A rms difference for the main-chain atoms can be obtained when etNOE interactions between non-neighboring residues occur over the length of the peptide. The global precision is higher (approximately 0.9 A rms difference) but is not correlated to global accuracy. A local definition of precision along the backbone appears to be a good indicator of the local accuracy.

Crystallography, X-Ray↗
PubMed2001

Echocardiographic transponder-guided catheter ablation feasibility and accuracy.

BACKGROUND: The utility of echocardiography for catheter guidance during percutaneous endocardial ablation is increasingly apparent. However, the technique is currently imperfect due to limitations in discerning the ablation electrode from other parts of the catheter shaft. PURPOSE: To examine the feasibility and accuracy of echocardiography-guided ablation using commercial ablation catheters fitted with a transponder to improve localization of the ablation electrode. METHODS: Fifteen healthy pigs and five pigs with chronic anterior myocardial infarction were studied. In healthy animals, echocardiographically distinct endocardial sites in right and left cardiac chambers were targeted for ablation. In infarcted animals, the left ventricular infarction border zone was targeted. Both intracardiac (ICE; 12.5 megahertz and 5 megahertz) and transesophageal echocardiographic (TEE) techniques were utilized. RESULTS: In healthy animals, transponder-guided ablation was feasible with each of the echocardiographic techniques. Accuracy was 82 % (45 of 55 lesions) with ICE-12.5 MHz, 87 % (27 of 31 lesions) with ICE-5 MHz, and 81 % (22 of 27 lesions) with TEE. In infarcted animals, the accuracy was 38 % (3 of 8 lesions) for ICE-5 MHz and 38 % (3 of 8 lesions) for TEE. Errant lesions in healthy animals were observed in earlier experiments, due to operator misinterpretation of the plane of imaging. Errant lesions in infarcted animals were observed throughout the experimental series, and may have been due to a variable relationship between echocardiographic and histologic infarction border zones. CONCLUSIONS: Echocardiographic transponder-guided catheter ablation is feasible. Accuracy for normal endocardial targets was excellent, less so for chronic infarction border.

Animals↗
PubMed2000

Accuracy of deadspace free ventilatory measurements for lung function testing in ventilated newborns: a simulation study.

OBJECTIVE: A deadspace free method based on simultaneous ventilatory measurements in the inspiratory and expiratory limb of the ventilator circuit was compared to the conventional endotracheal method where the flow is measured between ETT and Y-Piece. The aim of our study was to find out how the arrangement of this setup affects the measuring accuracy of 1) the ventilatory and 2) the lung mechanical parameters by means of a computer simulation. METHOD: The system consisting of ventilator tubes and lung was described in state space and the flow signals of endotracheal method, of deadspace free method and the pressure at the Y-piece were simulated in the time domain. To investigate the influence of the position of the pneumotachographs (PNTs) in the ventilator circuit on measuring accuracy, the distance d0 of the PNT from the Y-piece was varied between 0 and 900 mm. The respiratory compliance C, resistance R and inertance I were calculated by least square method using the simulated flow and pressure signals of both methods. RESULTS: Compared to the endotracheal method, with increasing d0, the tidal volume measured with the deadspace free method rose linearly, depending on the ratio between the compliance of the ventilator tubes to the respiratory compliance. The differences of C and R for both methods were acceptable (< 10%) if the distance between each PNT and the y-piece didn't exceed 200 mm and the shorter do the higher the measuring accuracy. The inertance could not be measured by this method with satisfactory accuracy if d0 was higher than 100 mm. IN CONCLUSION: The dead space free method can be used for accurate ventilatory measurements during mechanical ventilation. However, for lung mechanic measurements in very low birth weight infants the position of the PNTs must be as short as possible.

Airway Resistance↗
PubMed2002

Accuracy of student self-assessment ability compared to their own performance in a problem-based learning medical program: a correlation study.

OBJECTIVE: The purpose of this study was to evaluate the accuracy of self-assessment ability of students enrolled in a Problem-based Learning program. METHODS: Seventy students enrolled in their third year of a four-year program were invited to voluntarily participate in the study. Self-assessment questionnaire was used to measure the students' self-assessment ability on two different occasions: 1) prior to standardised oral examination in predicting their performance, and 2) following the examination estimating their performance. The accuracy of the self-assessment was investigated by the relation between self-assessment and performance of the students. RESULTS: Our study showed that self-assessment pre-examination was not accurate compared to performance at the oral examination (r ranging from 0.042 to 0.243). However, accuracy is slightly better when the student self-assesses his performance a posteriori, but the relation stays very low (r ranging from 0.257 to 0.334). CONCLUSION: According to our results, the students in the third year of a self-directed Problem-based Learning medical four year program demonstrated poor accuracy of the self-assessment when compared to their own performance.

Adult↗
PubMed2003

EEG-based communication and control: speed-accuracy relationships.

People can learn to control mu (8-12 Hz) or beta (18-25 Hz) rhythm amplitude in the EEG recorded over sensorimotor cortex and use it to move a cursor to a target on a video screen. In our current EEG-based brain-computer interface (BCI) system, cursor movement is a linear function of mu or beta rhythm amplitude. In order to maximize the participant's control over the direction of cursor movement, the intercept in this equation is kept equal to the mean amplitude of recent performance. Selection of the optimal slope, or gain, which determines the magnitude of the individual cursor movements, is a more difficult problem. This study examined the relationship between gain and accuracy in a 1-dimensional EEG-based cursor movement task in which individuals select among 2 or more choices by holding the cursor at the desired choice for a fixed period of time (i.e., the dwell time). With 4 targets arranged in a vertical column on the screen, large gains favored the end targets whereas smaller gains favored the central targets. In addition, manipulating gain and dwell time within participants produces results that are in agreement with simulations based on a simple theoretical model of performance. Optimal performance occurs when correct selection of targets is uniform across position. Thus, it is desirable to remove any trend in the function relating accuracy to target position. We evaluated a controller that is designed to minimize the linear and quadratic trends in the accuracy with which participants hit the 4 targets. These results indicate that gain should be adjusted to the individual participants, and suggest that continual online gain adaptation could increase the speed and accuracy of EEG-based cursor control.

Adult↗