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PubMedDate not supplied

A brief primer on automated signal detection.

BACKGROUND: Statistical techniques have traditionally been underused in spontaneous reporting systems used for postmarketing surveillance of adverse drug events. Regulatory agencies, pharmaceutical companies, and drug monitoring centers have recently devoted considerable efforts to develop and implement computer-assisted automated signal detection methodologies that employ statistical theory to enhance screening efforts of expert clinical reviewers. OBJECTIVE: To provide a concise state-of-the-art review of the most commonly used automated signal detection procedures, including the underlying statistical concepts, performance characteristics, and outstanding limitations, and issues to be resolved. DATA SOURCES: Primary articles were identified by MEDLINE search (1965-December 2002) and through secondary sources. STUDY SELECTION AND DATA EXTRACTION: All of the articles identified from the data sources were evaluated and all information deemed relevant was included in this review. DATA SYNTHESIS: Commonly used methods of automated signal detection are self-contained and involve screening large databases of spontaneous adverse event reports in search of interestingly large disproportionalities or dependencies between significant variables, usually single drug-event pairs, based on an underlying model of statistical independence. The models vary according to the underlying model of statistical independence and whether additional mathematical modeling using Bayesian analysis is applied to the crude measures of disproportionality. There are many potential advantages and disadvantages of these methods, as well as significant unresolved issues related to the application of these techniques, including lack of comprehensive head-to-head comparisons in a single large transnational database, lack of prospective evaluations, and the lack of gold standard of signal detection. CONCLUSIONS: Current methods of automated signal detection are nonclinical and only highlight deviations from independence without explaining whether these deviations are due to a causal linkage or numerous potential confounders. They therefore cannot replace expert clinical reviewers, but can help them to focus attention when confronted with the difficult task of screening huge numbers of drug-event combinations for potential signals. Important questions remain to be answered about the performance characteristics of these methods. Pharmacovigilance professionals should take the time to learn the underlying mathematical concepts in order to critically evaluate accumulating experience pertaining to the relative performance characteristics of these methods that are incompletely defined.

Automation↗

PubMed2003

[Multi-media computer-based chart: modern tool of clinical record keeping].

AIM: To design the program of computer multimedia case history (MCH) for collection, storage and analysis of information about the patient including diagnostic images; to test MCH for application in telemedical consulting and control over valid conduction of the treatment protocol. MATERIAL AND METHODS: Brief representation of information is reached by integrated multilevel placement of the data on common time axis. Dynamics of the selected parameters is represented as normalized diagrams in the same system axes. Electron tables are filled either by hand or import of the data from individual electron file of all the information about the patient. Diagnostic images and conclusions are obtained from local computer bases of the diagnostic units. Inexpensive commonly used computers allows one to input digital micro- and macrophotos, x-ray images, etc. Monitor information is available from the universal computer net directly from the monitors Geolink-M. RESULTS: MCH was tested in the Hematological Research Center of RAMS. In cooperation with Bryansk diagnostic center N 1 telemedical consulting and some data bases were perfected. The MCH system joints routine activity of the clinic without any problems raising quality of the patients management, facilitating the access to therapeutic and diagnostic information and its analysis. On-line breaking the limits of the controlled parameters and protocols is detected automatically. These events are emphasized by "blocking questions" which must be worked out by the user. The information on the patient can be fully stored on CD-ROM in line with the MCH program providing organization of the data. CONCLUSION: The system is introduced which collects medical information from various sourses and builds up comprehensive representation of the data on the same time axis. The system provides control over implimintation of the protocols of the patients' management, gives a convenient access to medical information, ensures its reliable storage and availability in case of the patients transfer to other medical institutions, facilitates analysis of clinical cases, conduction of medical consulting.

Computer Communication Networks↗

PubMed2000

Nasal decongestants for the common cold.

BACKGROUND: The common cold is a major and recurrent cause of morbidity, affecting children and adults two or more times each year. Nasal congestion is its commonest symptom, and many therapies are marketed for its relief. There is no meta-analysis of controlled clinical trials on the effects of nasal decongestants for the common cold. OBJECTIVES: To assess the efficacy of nasal decongestants at reducing the symptom of nasal congestion in adults and children with the common cold and to identify possible adverse effects associated with their use. SEARCH STRATEGY: MEDLINE, EMBASE and Current Contents were searched up to May 1999. Searching the Cochrane Acute Respiratory Infections Group's trials register, following the review citation trail from other references and contacting known principal investigators and pharmaceutical companies was also done. SELECTION CRITERIA: Randomised, placebo controlled trials of single-active oral and topical nasal decongestants in adults and children suffering from the common cold. DATA COLLECTION AND ANALYSIS: Data were independently extracted by two reviewers (DT and LB). All outcomes variables were continuous. Subjective outcomes were normalised to a common scale and a weighted mean difference (WMD) was calculated. A standardised mean difference (SMD) was calculated for the objective outcomes. MAIN RESULTS: Four studies in adults, but none in children, fitted all inclusion criteria. There was a significant 13% decrease in subjective symptoms after decongestant compared with placebo. This was supported by a significant decrease in nasal airways resistance. Repeated doses of nasal decongestant were not significantly better than placebo at relieving symptoms of nasal congestion. REVIEWER'S CONCLUSIONS: A single dose of nasal decongestant in the common cold is moderately effective for the short term relief of congestion in adults, while there is no evidence available to show benefit after repeated use over several days. These medications are not recommended for use in young children with the common cold.

Adult↗

PubMed2006

Haplotype analysis in the presence of informatively missing genotype data.

It is common to have missing genotypes in practical genetic studies, but the exact underlying missing data mechanism is generally unknown to the investigators. Although some statistical methods can handle missing data, they usually assume that genotypes are missing at random, that is, at a given marker, different genotypes and different alleles are missing with the same probability. These include those methods on haplotype frequency estimation and haplotype association analysis. However, it is likely that this simple assumption does not hold in practice, yet few studies to date have examined the magnitude of the effects when this simplifying assumption is violated. In this study, we demonstrate that the violation of this assumption may lead to serious bias in haplotype frequency estimates, and haplotype association analysis based on this assumption can induce both false-positive and false-negative evidence of association. To address this limitation in the current methods, we propose a general missing data model to characterize missing data patterns across a set of two or more markers simultaneously. We prove that haplotype frequencies and missing data probabilities are identifiable if and only if there is linkage disequilibrium between these markers under our general missing data model. Simulation studies on the analysis of haplotypes consisting of two single nucleotide polymorphisms illustrate that our proposed model can reduce the bias both for haplotype frequency estimates and association analysis due to incorrect assumption on the missing data mechanism. Finally, we illustrate the utilities of our method through its application to a real data set.

Algorithms↗

PubMed2002

Comparing clinical automated, medical record, and hybrid data sources for diabetes quality measures.

BACKGROUND: Little is known about the relative reliability of medical record and clinical automated data, sources commonly used to assess diabetes quality of care. The agreement between diabetes quality measures constructed from clinical automated versus medical record data sources was compared, and the performance of hybrid measures derived from a combination of the two data sources was examined. METHODS: Medical records were abstracted for 1,032 patients with diabetes who received care from 21 facilities in 4 Veterans Integrated Service Networks. Automated data were obtained from a central Veterans Health Administration diabetes registry containing information on laboratory tests and medication use. RESULTS: Success rates were higher for process measures derived from medical record data than from automated data, but no substantial differences among data sources were found for the intermediate outcome measures. Agreement for measures derived from the medical record compared with automated data was moderate for process measures but high for intermediate outcome measures. Hybrid measures yielded success rates similar to those of medical record-based measures but would have required about 50% fewer chart reviews. CONCLUSIONS: Agreement between medical record and automated data was generally high. Yet even in an integrated health care system with sophisticated information technology, automated data tended to underestimate the success rate in technical process measures for diabetes care and yielded different quartile performance rankings for facilities. Applying hybrid methodology yielded results consistent with the medical record but required less data to come from medical record reviews.

Aged↗

PubMed2002

The Frontlines of Medicine Project: a proposal for the standardized communication of emergency department data for public health uses including syndromic surveillance for biological and chemical terrorism.

The Frontlines of Medicine Project is a collaborative effort of emergency medicine (including emergency medical services and clinical toxicology), public health, emergency government, law enforcement, and informatics. This collaboration proposes to develop a nonproprietary, "open systems" approach for reporting emergency department patient data. The common element is a standard approach to sending messages from individual EDs to regional oversight entities that could then analyze the data received. ED encounter data could be used for various public health initiatives, including syndromic surveillance for chemical and biological terrorism. The interlinking of these regional systems could also permit public health surveillance at a national level based on ED patient encounter data. Advancements in the Internet and Web-based technologies could allow the deployment of these standardized tools in a rapid time frame.

Biological Warfare↗

PubMed1988

Families of lines: random effects in linear regression analysis.

Laboratory experiments often involve two groups of subjects, with a linear phenomenon observed in each subject. Simple linear regression as propounded in standard textbooks is inadequate to treat this experimental design, particularly when it comes to dealing with random variation of slopes and intercepts among subjects. The author describes several techniques that can be used to compare two independent families of lines and illustrates their use with laboratory data. The methods are described tutorially, compared, and discussed in the context of more sophisticated and more naive approaches to this common data-analytic problem. Technical details are supplied in APPENDIX A.

Adolescent↗

PubMed2001

Analysis of complex survey data using SAS.

Commonly used statistical methods and software packages typically assume that observations are independent and identically distributed and fail to account for complex sampling designs when present. I suggest an approach to analyzing complex survey data in SAS, using weighted generalized estimating equations. Limited Monte Carlo simulations support the method. An example demonstrates application of the method and compares results to those from software commonly used in the analysis of complex survey data.

Aged↗

PubMed2003

Bagging tree classifiers for laser scanning images: a data- and simulation-based strategy.

Diagnosis based on medical image data is common in medical decision making and clinical routine. We discuss a strategy to derive a classifier with good performance on clinical image data and to justify the properties of the classifier by an adapted simulation model of image data. We focus on the problem of classifying eyes as normal or glaucomatous based on 62 routine explanatory variables derived from laser scanning images of the optic nerve head. As learning sample we use a case-control study of 98 normal and 98 glaucomatous subjects matched by age and sex. Aggregating multiple unstable classifiers allows substantial reduction of misclassification error in many applications and bench mark problems. We investigate the performance of various classifiers for the clinical learning sample as well as for a simulation model of eye morphologies. Bagged classification trees (bagged-CTREE) are compared to single classification trees and linear discriminant analysis (LDA). We additionally compare three estimators of misclassification error: 10-fold cross-validation, the 0.632+ bootstrap and the out-of-bag estimate. In summary, the application of our strategy of a knowledge-based decision support shows that bagged classification trees perform best for glaucoma classification.

Case-Control Studies↗

PubMedDate not supplied

A field-compatible method for interpolating biopotentials.

Mapping of bioelectric potentials over a given surface (e.g., the torso surface, the scalp) often requires interpolation of potentials into regions of missing data. Existing interpolation methods introduce significant errors when interpolating into large regions of high potential gradients, due mostly to their incompatibility with the properties of the three-dimensional (3D) potential field. In this paper, an interpolation method, inverse-forward (IF) interpolation, was developed to be consistent with Laplace's equation that governs the 3D field in the volume conductor bounded by the mapped surface. This method is evaluated in an experimental heart-torso preparation in the context of electrocardiographic body surface potential mapping. Results demonstrate that IF interpolation is able to recreate major potential features such as a potential minimum and high potential gradients within a large region of missing data. Other commonly used interpolation methods failed to reconstruct major potential features or preserve high potential gradients. An example of IF interpolation with patient data is provided to illustrate its applicability in the actual clinical setting. Application of IF interpolation in the context of noninvasive reconstruction of epicardial potentials (the "inverse problem") is also examined.

Action Potentials↗

PubMed2003

The structure of self-reported emotional experiences: a mixed-effects Poisson factor model.

Multivariate count data are commonly analysed by using Poisson distributions with varying intensity parameters, resulting in a random-effects model. In the analysis of a data set on the frequency of different emotion experiences we find that a Poisson model with a single random effect does not yield an adequate fit. An alternative model that requires as many random effects as emotion categories requires high-dimensional integration and the estimation of a large number of parameters. As a solution to these computational problems, we propose a factor-analytic Poisson model and show that a two-dimensional factor model fits the reported data very well. Moreover, it yields a substantively satisfactory solution: one factor describing the degree of pleasantness and unpleasantness of emotions and the other factor describing the activation levels of the emotions. We discuss the incorporation of covariates to facilitate rigorous tests of the random-effects structure. Marginal maximum likelihood methods lead to straight-forward estimation of the model, for which goodness-of-fit tests are also presented.

Arousal↗

PubMed2002

Methods for claims-based pharmacoeconomic studies in psychosis.

Pharmacoeconomic studies using claims data are frequently employed to compare the healthcare costs associated with competing drugs. Different methodological approaches with varying limitations for evaluating claims data are reviewed within the context of psychosis. Intent-to-treat paradigms and mirror-image designs have limitations that can bias comparisons of health resource use and can be addressed through the use of drug treatment episodes. Health resource use is better measured in financial rather than volume amounts, to account for service intensity. However, financial measures reported in claims records need to be carefully chosen. Between-group comparisons are frequently affected by selection bias, and within-group comparisons are often limited by period bias. While selection bias can be addressed by controlling for patient factors such as disease severity, and period bias by controlling for trend, devising appropriate control measures from the limited information in claims data can be challenging. Healthcare data are often skewed, which affects statistical testing. While skewed data are commonly handled through log transformation, this method has serious limitations, potentially distorting pharmacoeconomic comparisons. Determining the most appropriate methods for claims-based data involves careful evaluation of the alternate approaches to best achieve the goals of a pharmacoeconomic investigation.

Antipsychotic Agents↗

PubMed1984

Stabilized binary hierarchic classifier in cytopathologic diagnosis.

A binary tree classifier (BTC) algorithm for computer-assisted cell image analysis has been developed that overcomes the problem of overtraining due to inadequate sample size/dimensionality ratio at the higher-order nodes of a hierarchic decision structure. Provisions have been introduced that ensure that decision rules created at each node are based on samples representative of the subpopulation routed to the node. These provisions eliminate problems caused by truncation effects resulting from the application of decision rules at preceding decision nodes. The BTC performs better than do single-stage classifiers in situations where the categories' mean vectors are not well separated and no equality of covariance matrices exists. In applications in which noticeable deterioration of classifier performance on test-set data is common, the classification success rate of the BTC algorithm is not statistically significantly different between the training-set and test-set data.

Cells↗

PubMed1977

Evidence of a specific nidation site in ruminants.

The site of umbilical cord attachment in ruminants indicates the limited segment of the uterus where the blastocyst attachment occurs and could have potential significance for locating presumptive nidation sites. Measurements of the site of cord attachment were made on impala (Aepyceros melampus) and common duiker (Sylvicapra grimmia) at several stages of gestation. Both implant only in the right uterine horn although they ovulate from either ovary. Relative to uterine length, cord attachment in impala is somewhat closer to the cervix than it is in common duiker. As pregnancy advances in common duiker, the relative position of cord attachment becomes closer to the tubal end. This relationship was not seen in impala and may perhaps to be attributed inadequate data. Upon extrapolation of the data from common duiker, a presumptive attachment area is suggested for this species. This region is located at about 41% of the distance from the internal cervical os to the uterotubal junction. Similar cord attachment data could be used in any ruminant species to indicate the existence and location of a specific nidation site.

Animals↗

PubMed2003

Three-dimensional volume rendering of multidetector-row CT data: applicable for emergency radiology.

Multidetector-row computed tomography (MD-CT) not only creates new opportunities but also challenges for medical imaging. Isotropic imaging allows in-depth views into anatomy and disease but the concomitant dramatic increase of image data requires new approaches to visualize, analyze and store CT data. The common diagnostic reviewing process slice by slice becomes more and more time consuming as the number of slice increases, while on the other hand CT volume data sets could be used for three-dimensional visualization. These techniques allow for comprehensive interpretation of extent of fracture, amount of dislocation and fragmentation in a three-dimensional highly detailed setting. Further more, using minimal invasive techniques like CT angiography, new opportunities for fast emergency room patient's work up arise. But the most common application is still trauma of the musculoskeletal system as well as face and head. The following is a brief review of recent literature on volume rendering technique and some exemplary applications for the emergency room.

Angiography↗

PubMed2006

Geocoding in cancer research: a review.

There is now widespread agreement that geographic identifiers (geocodes) should be assigned to cancer records, but little agreement on their form and how they should be assigned, reported, and used. This paper reviews geocoding practice in relation to major purposes and discusses methods to improve the accuracy of geocoded cancer data. Differences in geocoding methods and materials introduce errors of commission and omission into geocoded data. A common source of error comes from the practice of using digital boundary files of dubious quality to place addresses into areas of interest. Geocoded data are linked to demographic, environmental, and health services data, and each data type has unique accuracy considerations. In health services applications, the accuracy of distances computed from geocodes can differ markedly. Privacy and confidentiality issues are important in the use and release of geocoded cancer data. When masking methods are used for disclosure limitation purposes, statistical methods must be adjusted for the locational uncertainty of geocoded data. We conclude that selection of one particular type of geographic area as the geocode may unnecessarily constrain future work. Therefore, the longitude and latitude of each case is the superior basic geocode; all other geocodes of interest can be constructed from this basic identifier.

Biomedical Research↗

PubMed2000

Validation of self-reported chronic conditions and health services in a managed care population.

BACKGROUND: Self-reported data are commonly used to estimate the prevalence of health conditions and the use of preventive health services in the population, but the validity of such data is often questioned. METHODS: The Behavioral Risk Factor Survey (BRFS) was admin istered by telephone to a stratified, random sample of health maintenanc e organization (HMO) subscribers in Colorado in 1993, and self-reports w ere compared with HMO medical records for 599 adults aged >21. Sensitivity and specificity were calculated for three chronic conditions and use of six preventive services. RESULTS: Sensitivity was highest for hypertension (83%), moderate for diabetes (73%), and lowest for hypercholesterolemia (59%); specificity was >80% for all three conditions. Sensitivity ranged from 86% to 99% for influenza immunization, clinical breast examination, blood cholesterol screening, mammography, Pap test, and blood pressure screening; specificity was <75% for all preventive services. CONCLUSIONS: Self-reports are reasonably accurate for certain chronic conditions and for routine screening exams and can provide a useful estimate for broad measures of population prevalence.

Adult↗

PubMed1996

[A simplified method for the statistical evaluation of experimental data].

A simplified method excluding the use of special tables is proposed for rapid determination of the confidence interval values in biomedical or other experimental studies. The method is based on a simplified approximation of quantitative relation of experimental data with commonly employed standard methods. Approximation formula has been calculated to warrant rapid memorizing.

Data Interpretation, Statistical↗