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PubMed1996

A simple method for comparing correlated ROC curves using incomplete data.

Comparative studies of the accuracy of diagnostic procedures often use a paired design to gain in efficiency. Standard methods for analysing data from paired designs require complete observations. In many studies, however, one of the test results may be missing for some patients. In this paper, we propose a simple correction to the existing complete data methods to compare areas under ROC curves derived from paired designs. The approach makes it possible to use the entire available data set in carrying out the comparison, provided that the probability of having both tests does not depend on the test results. As an illustration, we apply our method to the analysis of data from prospective comparison of MRI and ultrasound in detecting periprostatic invasion.

Data Interpretation, Statistical↗
PubMed2002

High-throughput SELEX SAGE method for quantitative modeling of transcription-factor binding sites.

The ability to determine the location and relative strength of all transcription-factor binding sites in a genome is important both for a comprehensive understanding of gene regulation and for effective promoter engineering in biotechnological applications. Here we present a bioinformatically driven experimental method to accurately define the DNA-binding sequence specificity of transcription factors. A generalized profile was used as a predictive quantitative model for binding sites, and its parameters were estimated from in vitro-selected ligands using standard hidden Markov model training algorithms. Computer simulations showed that several thousand low- to medium-affinity sequences are required to generate a profile of desired accuracy. To produce data on this scale, we applied high-throughput genomics methods to the biochemical problem addressed here. A method combining systematic evolution of ligands by exponential enrichment (SELEX) and serial analysis of gene expression (SAGE) protocols was coupled to an automated quality-controlled sequence extraction procedure based on Phred quality scores. This allowed the sequencing of a database of more than 10,000 potential DNA ligands for the CTF/NFI transcription factor. The resulting binding-site model defines the sequence specificity of this protein with a high degree of accuracy not achieved earlier and thereby makes it possible to identify previously unknown regulatory sequences in genomic DNA. A covariance analysis of the selected sites revealed non-independent base preferences at different nucleotide positions, providing insight into the binding mechanism.

Base Sequence↗
PubMed1997

The effect of a rapid kit for detection of streptococcal pharyngitis on the accuracy of the physicians' diagnoses.

BACKGROUND: In the last decade, the accuracy of rapid tests for detection of group A streptococcal antigen was evaluated in laboratory and clinical settings, and the tests were suggested as an alternative to the traditional throat culture. METHODS: We evaluated 19 patients with a preliminary diagnosis of nonstreptococcal pharyngitis and 13 patients with a preliminary diagnosis of streptococcal pharyngitis. The physician performed a rapid latex agglutination test (Detect A Strep), took throat culture from all of the patients, reconsidered the preliminary diagnosis, and made a working diagnosis. A clinical score was calculated for each patient during data analysis. The accuracy of the physicians' preliminary diagnoses was compared with the accuracy of the scoring system, with the accuracy of the latex agglutination test, and with the accuracy of the physicians' working diagnoses. RESULTS: The scoring system, the physicians' preliminary diagnoses, the latex agglutination test, and the physicians' working diagnoses correlated significantly with throat culture results (p < or = 0.05). The efficiency of the physicians' preliminary diagnoses was 75% compared with an efficiency of 69% of the clinical scoring system, an efficiency of 66% of the latex agglutination test, and an efficiency of 69% of the physicians' working diagnoses. The physician changed the preliminary diagnosis only for two patients as a result of the latex agglutination test results; ironically, however, the preliminary diagnosis was correct in both of these cases. CONCLUSION: The use of a rapid test for the diagnosis of group A streptococcal antigen under normal working conditions did not improve the accuracy of the physician's diagnosis, so the use of the latex agglutination test in this study was not cost-effective.

Adult↗
PubMed1989

A simple method to detect and estimate heterogeneity: application to Huntington disease, diabetes, and HIV seroconversion.

The traditional method for calculating risk in prospective and retrospective studies is based on the assumption that the study population is homogeneous. Risk is therefore estimated as an overall average for the entire population, when in fact some individuals may be at high risk and others at little or no risk. This paper introduces an alternate approach to risk estimation. The calculations are equally simple and utilize the same data. Yet, the new approach allows for heterogeneity and can detect it when it exists. The new method was applied to HIV seroconversion data from a follow-up study, age-at-onset distribution for Huntington disease, and age-specific prevalence of insulin-treated diabetes. These analyses were intended to demonstrate both applicability of the method to different types of data and the accuracy of the estimates when compared with the known parameters. The HIV analysis predicted a high-risk subgroup constituting about 17% of the cohort. This estimate closely approximates the actual 16% who reportedly engaged in high-risk activities and had a 15-fold higher seroconversion rate than the rest of the cohort. There is no evidence from genetic linkage studies for heterogeneity in Huntington disease. The present results, however, suggested that 14%-18% of individuals who are susceptible to the disease have a much lower risk than others. Diabetes data was chosen because the model is clearly too simplistic for this disease, and the analysis did reveal lack of fit of the model.

Adult↗
PubMed1980

Measurement accuracy of the mandibular kinesiograph--a computerized study.

Today's high-technology electronic and computer techniques have been applied to the long-standing problem of tracking mandibular movement and skeletal relation in research and diagnosis of mandibular function/dysfunction. The measurement established that within an area known as "clinical space" where most diagnostic data is derived, the linearity and quantitative accuracy ranged from error of 0 mm at intercuspation to 0.5 mm at worst error. This order of accuracy provides data that is qualitatively and quantitatively useful for research and diagnosis without the need for further correction. Computer processing further reduces the worst anywhere within the clinical space to 0.1 mm. Geometric skewing of the trace patterns that occur while taking data at mouth openings beyond clinical space (though not pronounced enough to affect the qualitative usefulness of the data) is readily corrected by computer processing. A microcomputer attached to the K5-R corrects the skew in real-time so that the data are displayed to an accuracy within 1.5% of exact values or a worst-case error less than 0.5 mm for a 30 mm vertical opening. When tested against a computer-controlled electronic measuring system, the accuracy and linearity parameters of the trace patterns confirmed the validity of the MKG recordings as precise representations of mandibular movement at the incisor point.

Computers↗
PubMed1997

Chest radiograph interpretation of Pneumocystis carinii pneumonia, bacterial pneumonia, and pulmonary tuberculosis in HIV-positive patients: accuracy, distinguishing features, and mimics.

The purpose of this study was to assess the accuracy of chest x-ray (CXR) interpretation in the diagnosis of pneumocystis carinii pneumonia (PCP), bacterial pneumonia (BP), and pulmonary tuberculosis (TB) in human immunodeficiency virus (HIV)-positive patients and to identify the frequency with which these infections mimic one another radiographically. The admitting CXRs of 153 HIV-positive patients with laboratory proven BP (n = 71), PCP (n = 73), and TB (n = 9) and those of 10 HIV-positive patients with no active disease were reviewed retrospectively and independently by three radiologists who were blinded to clinical and laboratory data. Median percent accuracies were as follows: TB, 84%; PCP, 75%; BP, 64%; and no active disease, 100%. Fifteen of 153 cases (9.8%) were shown to mimic other infections radiographically. A confident and accurate diagnosis can be made radiographically in the majority of cases of PCP, BP, and TB in HIV-positive patients at the time of hospitalization. In approximately 10% of cases, these infections may mimic one another radiographically.

AIDS-Related Opportunistic Infections↗
PubMed2005

Comparison of 99mTc-sestamibi/18FDG DISA SPECT with PET for the detection of viability in patients with coronary artery disease and left ventricular dysfunction.

PURPOSE: Dual-isotope simultaneous acquisition (DISA) single-photon emission computed tomography (SPECT) is an attractive technique as it permits assessment of both myocardial glucose metabolism and perfusion within a single session, but few data on its accuracy for the assessment of viability are available as yet. In the present study, DISA SPECT was compared with positron emission tomography (PET) for the detection of myocardial viability in normal and dysfunctional left ventricular (LV) myocardium. METHODS: Fifty-eight patients with chronic coronary artery disease and LV dysfunction (LV ejection fraction 33+/-12%) were studied. Patients underwent a 1-day dipyridamole stress 99mTc-sestamibi/18F-fluorodeoxyglucose (18FDG) DISA SPECT and 13N-ammonia/18FDG PET protocol. Within 1 week, resting MRI was performed to assess contractile function. Comparison of PET and SPECT data was performed using both visual and quantitative analysis. RESULTS: The correlation of normalised activities of the flow tracers 99mTc-sestamibi and 13N-ammonia was good (r = 0.82; p < 0.001). The correlation between the two 18FDG studies was also good (r = 0.83; p < 0.001). The agreement for the assessment of viability for all segments between DISA SPECT and PET was 82%, with a kappa-statistic of 0.59 (95% CI 0.53-0.64), without a significant difference; in dysfunctional segments only, the agreement was 82%, with a kappa-statistic of 0.63 (95% CI 0.56-0.70), without a significant difference. When the DISA SPECT data were analysed visually, the agreement between DISA SPECT and PET was 83%, with a kappa-statistic of 0.58 (95% CI 0.52-0.63), without a significant difference. Moreover, there was no significant difference between visual and quantitative DISA SPECT analysis for the detection of viability. CONCLUSION: This study shows an overall good agreement between 99mTc-sestamibi/18FDG DISA SPECT and PET for the assessment of myocardial viability in patients with severe LV dysfunction. Quantitative or visual analysis of the SPECT data did not influence the agreement with PET, suggesting that visual assessment may be sufficient for clinical purposes.

Adult↗
PubMed2006

Antibiotics versus placebo for acute bacterial conjunctivitis.

BACKGROUND: There are concerns about whether antibiotic therapy confers significant clinical benefit in the treatment of acute bacterial conjunctivitis. OBJECTIVES: The aim of this review was to assess the benefit and harm of antibiotic therapy in the management of acute bacterial conjunctivitis. SEARCH STRATEGY: We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (which contains the Cochrane Eyes and Vision Group Trials Register), MEDLINE, EMBASE, SIGLE, NRR, PubMed and the reference lists of identified trial reports. We used the Science Citation Index to look for articles that cited the relevant studies, and we contacted investigators and pharmaceutical companies for information about additional trials. SELECTION CRITERIA: We included double masked randomised controlled trials in which any form of antibiotic treatment had been compared with placebo in the management of acute bacterial conjunctivitis. This included topical, systemic and combination (for example, antibiotics and steroids) antibiotic treatments. DATA COLLECTION AND ANALYSIS: One author extracted data and the accuracy was checked by a second author. MAIN RESULTS: This review includes five trials which randomised a total of 1034 participants. One further trial is currently 'awaiting assessment'. This has been published in abstract form and has yet to be fully reported. Three of the trials have been conducted on a selected specialist care patient population and the two more recent trials have been conducted in a community care setting. The trials were heterogeneous in terms of their inclusion and exclusion criteria, the nature of the intervention, and the outcome measures assessed. Meta-analyses of data on clinical and microbiological remission rates reveal that topical antibiotics are of benefit in improving early (days 2 to 5) clinical (RR 1.24, 95% CI 1.05 to 1.45) and microbiological (RR 1.77, 95% CI 1.23 to 2.54) remission rates; later (days 6 to 10) data reveal that these early advantages in clinical (RR 1.11, 95% CI 1.02 to 1.21) and microbiological cure rates are reduced (RR 1.56, 95% CI 1.17 to 2.09), but persist. Most cases however resolve spontaneously with clinical remission being achieved in 65% (95% CI 59 to 70) by days 2 to 5 in those receiving placebo. No serious outcomes were reported in either the active or placebo arms of these trials, indicating that important sight-threatening complications are an infrequent occurrence. AUTHORS' CONCLUSIONS: Acute bacterial conjunctivitis is frequently a self-limiting condition, but the use of antibiotics is associated with significantly improved rates of clinical and microbiological remission.

Acute Disease↗
PubMed1998

Fast accurate iterative reconstruction for low-statistics positron volume imaging.

A fast accurate iterative reconstruction (FAIR) method suitable for low-statistics positron volume imaging has been developed. The method, based on the expectation maximization-maximum likelihood (EM-ML) technique, operates on list-mode data rather than histogrammed projection data and can, in just one pass through the data, generate images with the same characteristics as several ML iterations. Use of list-mode data preserves maximum sampling accuracy and implicitly ignores lines of response (LORs) in which no counts were recorded. The method is particularly suited to systems where sampling accuracy can be lost by histogramming events into coarse LOR bins, and also to sparse data situations such as fast whole-body and dynamic imaging where sampling accuracy may be compromised by storage requirements and where reconstruction time can be wasted by including LORs with no counts. The technique can be accelerated by operating on subsets of list-mode data which also allows scope for simultaneous data acquisition and iterative reconstruction. The method is compared with a standard implementation of the EM-ML technique and is shown to offer improved resolution, contrast and noise properties as a direct result of using improved spatial sampling, limited only by hardware specifications.

Image Processing, Computer-Assisted↗
PubMed1982

[Comparative studies on the determination of thiocyanate in biological materials (author's transl)].

On verifying methods for the determination of thiocyanate in biological materials, we started from the technique as described by Boxer and Rickards [5]. In different methods, the accuracy of the data obtained is affected by the deproteinization process or interfered with iron (III) ions or pyridine/benzidine, the deproteinization process being the decisive factor. This holds true especially in respect of interfering factors that remain in the supernatant (low-molecular amino compounds) and in respect of the coprecipitation of thiocyanate, the nature of the respective biological material playing an important part in both cases. At higher thiocyanate concentrations, pretreatment with a denaturing agent that is commonly used to deproteinization of human and bovine sera involves a small loss of thiocyanate due to coprecipitation. In case of high demands on reproducibility and accuracy of the analytical results, and in case of special analytical problems, isolation of thiocyanate is absolutely necessary (chromatography on Sephadex, aeration after conversion to hydrogen cyanide). Gas chromatography is suited for determining thiocyanate in whole blood.

Amino Acids↗
PubMed2004

Transplant data: sources, collection, and caveats.

By examining the sources, quality and organization of transplant data available, as well as making observations about data reporting patterns and accuracy, we hope to improve understanding of existing results, help researchers with study design and stimulate new exploratory initiatives. The primary data source, collected by the OPTN, has benefited from extensive recent technological advances. Transplant professionals now report patient and donor data more easily, quickly, and accurately, improving data timeliness and precision. Secondary sources may be incorporated, improving the accuracy and expanding the scope of analyses. For example, auxiliary mortality data allows more accurate survival analysis and conclusions regarding the completeness of center-reported post-transplant follow-up. Furthermore, such sources enable examination of outcomes not reported by centers, such as mortality after waiting list removal, providing more appropriate comparisons of waiting list and post-transplant mortality. Complex collection and reporting processes require specific analytical methods and may lead to potential pitfalls. Patterns in the timing of reporting adverse events differ from those for 'positive' events, yielding the need for care in choosing cohorts and censor dates to avoid bias. These choices are further complicated by the use of multiple sources of data, with different time lags and reporting patterns.

Humans↗
PubMed2003

Head up versus head down: the costs of imprecision, unreliability, and visual clutter on cue effectiveness for display signaling.

We conducted 2 experiments to investigate the clutter-scan trade-off between the cost of increasing clutter by overlaying complex information onto the forward field of view using a helmet-mounted display (HMD) and the cost of scanning when presenting this information on a handheld display. In the first experiment, this trade-off was examined in terms of the spatial accuracy of target cuing data in a relatively sparse display; in the second, the spatial accuracy of the cue was varied more radically in an information-rich display. Participants were asked to detect and identify targets hidden in the far domain while performing a monitoring task in the near domain using either an HMD or a handheld display. The results revealed that on a sparse display, the reduced scanning from the HMD presentation of cuing out-weighed the costs of clutter for cued targets, regardless of cue precision, but no benefit was found for uncued targets. When the HMD displayed task-irrelevant information, however, target detection was hindered by the extraneous clutter in the forward field of view relative to the handheld display condition, and this cost of clutter increased as the amount of data that needed to be inspected increased. Potential applications of this research include the development of design considerations for head-up displays for aviation and military applications.

Aerospace Medicine↗
PubMed1983

A comparison of automated data collection and manual data collection for toxicology studies.

Automated data collection was compared with manual data collection in terms of accuracy and man-hours devoted to data manipulation and checking. The comparison was based on experience with an automated data collection system (DOLPHIN)TM1 developed at Toxigenics for use in conducting toxicological studies. It was found that on-line data collection increases the quality of the data gathered because: 1) it facilitates scientific observation by displaying historical data and statistics on changes since the last observation period; 2) it virtually eliminates errors due to oversight and transcription; 3) it allows more careful monitoring of the course of the study by providing immediate access to interim summary statistics; 4) it provides complete documentation of all changes made to the data after initial collection. In addition, automated data collection enables more rapid completion of the final report of results because: 1) fewer departmental transfers are required; 2) auditing by Quality Assurance (Q.A.) personnel is facilitated.

Data Collection↗
PubMed1985

Computation of radiation dose distributions for shielded cervical applicators.

While cervical applicators with shielded ovoids are used widely in brachytherapy, we know of no system for calculating dose distributions for them. For shielded sources, because of a lack of symmetry and because of a rapid variation of dose as a function of position relative to the source, extensive measured data in three dimensions are required. In the method we have developed, the dose at a given point from a source in a shielded ovoid is calculated by multiplying the dose from an unshielded source by the "effective attenuation factor" of the shields. The latter quantity is obtained by linear-interpolation in a three-dimensional table generated from measurements described in an earlier paper. The unshielded-source dose is calculated as the product of source strength, time of implant, distance-dependent geometry factor and a tabulated quantity called the "relative dose rate factor". Relative dose rate factor is obtained by dividing measured dose rate by the product of geometry factor and source strength. Division by the geometry factor reduces the amount of data required with respect to accuracy in linear-interpolation. Input localization data must include not only the position of the end points defining the source but also a third reference point to define the orientation of the shields.

Brachytherapy↗
PubMed2002

Impact of graphical user interface screen features on computer task accuracy and speed in a cohort of patients with age-related macular degeneration.

PURPOSE: To investigate the impact of graphical user interface screen features on computer task performance in patients with age-related macular degeneration (AMD). DESIGN: Interventional case series. METHODS: Eighteen patients with visual impairment due to AMD were recruited from the Bascom Palmer Eye Institute Low Vision Clinic. Each patient underwent evaluation of visual acuity using the Early Treatment Diabetic Retinopathy Study protocol, contrast sensitivity using a Pelli-Robson chart, binocular simultaneous visual field using the Esterman program on an automated perimeter, and color vision using Farnsworth D-15. Each subject then completed computer icon identification tasks while the following screen features of the graphical user interface were varied: size of icons displayed, icon set size (number of icons displayed), and background color. Each patient performed all 125 computer tasks with each of five icon sizes (9.2 mm, 14.6 mm, 23.2 mm, 36.8 mm, 58.3 mm), each of five icon set sizes (2, 3, 4, 5, 6), and each of five different background colors (black, white, red, green, blue) in a randomly ordered fashion. Relationships between computer task performance (accuracy and speed) and graphical user interface screen features were studied. RESULTS: Icon size and icon set size are significantly associated with computer task accuracy (P <.001), whereas background color is not a significant predictor of task accuracy (P =.63). The impact of icon size on accuracy is nonlinear, with the data indicating that no additional improvement in accuracy is associated with increasing the icon size beyond 23.2 mm. The impact of icon set size on accuracy is linear, with a smaller icon set size significantly associated with greater computer accuracy. A larger icon size is significantly associated with a shorter time to task completion (P =.001); this relationship is largely linearly related to icon size. There was no significant impact of background color (P =.11) or set size (P =.37) on time to task completion. CONCLUSIONS: Modifications of graphical user interface design may permit improved computer task performance among patients with visual impairment due to AMD.

Adult↗
PubMed2002

Detecting and quantifying sunflower oil adulteration in extra virgin olive oils from the eastern mediterranean by visible and near-infrared spectroscopy.

One hundred and thirty-eight oil samples have been analyzed by visible and near-infrared transflectance spectroscopy. These comprised 46 pure extra virgin olive oils and the same oils adulterated with 1% (w/w) and 5% (w/w) sunflower oil. A number of multivariate mathematical approaches were investigated to detect and quantify the sunflower oil adulterant. These included hierarchical cluster analysis, soft independent modeling of class analogy (SIMCA method), and partial least squares regression (PLS). A number of wavelength ranges and data pretreatments were explored. The accuracy of these mathematical models was compared, and the most successful models were identified. Complete classification accuracy was achieved using 1st derivative spectral data in the 400-2498 nm range. Prediction of adulterant content was possible with a standard error equal to 0.8% using 1st derivative data between 1100 and 2498 nm. Spectral features and chemical literature were studied to isolate the structural basis for these models.

Food Contamination↗
PubMed2006

Quantitative standards for fetal and neonatal autopsy.

Growth curves are essential for determining whether growth parameters lie within normal ranges. In the case of fetal and neonatal autopsy, relevant data are scattered across many publications, and few sources examine a large enough sample to be considered definitive. To ameliorate these inadequacies, regressions were created incorporating data from multiple sources both to increase accuracy and to condense available data into a single standard. When measurements were not well studied, the best available published standards are given. These regressions provide a valuable tool for clinicians who need to understand the significance of measurements obtained during autopsy.

Anthropometry↗
PubMed2000

The future is coming and it will be amazing: computers in dentistry.

The computer in the dental office, especially at chairside, provides both "high tech" and "high touch" benefits. Single entry of data has the benefit of accuracy and time savings. It also makes data available regarding the practice in an easy-to-use fashion. Some suggestions are offered to those contemplating the addition of a computer system to their offices.

Budgets↗