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At least 919 records · Page 51Linked to original sources
PubMed2004

A semiparametric bootstrap approach to correlated data analysis problems.

In this note, we outline a simple to use yet powerful bootstrap algorithm for handling correlated outcome variables in terms of either hypothesis testing or confidence intervals using only the marginal models. This new method can handle combinations of continuous and discrete data and can be used in conjunction with other covariates in a model. The procedure is based upon estimating the family-wise error (FWE) rate and then making a Bonferroni-type correction. A simulation study illustrates the accuracy of the algorithm over a variety of correlation structures.

Algorithms↗
PubMed1990

Empirical considerations in orthopaedic research design and data analysis. Part I: Strategies in research design.

Empirical investigations have a direct effect on future therapeutic interventions. Thus, the advancement of any field of medicine is dependent upon the critical evaluation of research. Careful research design by investigators is necessary to yield meaningful, significant data. A clear understanding of basic statistical relationships is necessary for the clinician to evaluate the significance and quality of the scientific literature.

Humans↗
PubMed2003

Evaluation of leachate composition by multivariate data analysis (MVDA).

Landfills generate emissions in the form of gas and leachate. The emissions are often measured within monitoring programmes. It is likely that the requirements of such monitoring programmes can be extended in the future, particularly in light of the increased interest in specific organic substances. Multivariate data analyses (MVDA) have been used to evaluate the possibility of predicting the content of specific organic substances from more common analyses. The results indicate that this is possible for a specific leachate. MVDA can also be used to reduce the number of analyses performed within existing monitoring programmes while retaining information about all the variables formerly included in the programmes.

Environmental Monitoring↗
PubMed2006

Discovering dangerous patterns in long-term ambulatory ECG recordings using a fast QRS detection algorithm and explorative data analysis.

The next two decades will see dramatic changes in the health needs of the world's populations with chronic diseases as the leading causes of disability, according to recent World Health Organization reports. Increases in the senior population living "confined" in domestic area are also expected producing a steep increase in the need for long-term monitoring and home care services. Independently of the particular features and specific architectures, long-term monitoring systems usually produce a large amount of data to be analyzed and inspected by the practitioners and in particular by the cardiologists dealing with ECG recordings analysis. This problem is well known and regards also the traditional holter-based practice. In this paper we present a program for discovering patterns in ECG recordings, to be considered as a medical decision-making support. Computational methods are based on a QRS detector especially designed for noisy applications followed by a parameters space reduction operated by the KL transform modified on a "user-fit" basis. Events characterization is based on a recently introduced clustering method, called KHM (K-harmonic means). The most representative beat families and the corresponding prototypes (physiological and pathological) are then presented to the user through appropriate graphics to facilitate an easy and fast interpretation. We tested the QRS detection algorithm using the MIT-BIH arrhythmia database. Our method produced 565 false positive beats and 379 false negative beats and a total detection failure of 0.85% considering all the 109.809 annotated beats in the database. While a clinical experimentation of our program is on the way, we used the VALE Database to perform a preliminary evaluation of the methods used for data exploration (PCA, KHM). Considering the entire database, we succeeded in identifying pathological clusters in 97% of the cases.

Algorithms↗
PubMed1995

Problems and prediction in survival-data analysis.

Twenty-one years after its appearance, Cox's 1972 paper on 'Regression models and life tables' continues to be one of the most frequently cited publications in the scientific and medical literature. The proportional-hazards model and partial-likelihood technique have been applied to thousands of data sets, not always appropriately, and have motivated hundreds of theoretical studies, not always relevant. Recent developments are reviewed and continuing problems discussed, especially with respect to predictive inference. The accuracy of model-based predictions, and how they compare with consultants' judgements are investigated by means of an example.

Humans↗
PubMed2001

Drug design by machine learning: support vector machines for pharmaceutical data analysis.

We show that the support vector machine (SVM) classification algorithm, a recent development from the machine learning community, proves its potential for structure-activity relationship analysis. In a benchmark test, the SVM is compared to several machine learning techniques currently used in the field. The classification task involves predicting the inhibition of dihydrofolate reductase by pyrimidines, using data obtained from the UCI machine learning repository. Three artificial neural networks, a radial basis function network, and a C5.0 decision tree are all outperformed by the SVM. The SVM is significantly better than all of these, bar a manually capacity-controlled neural network, which takes considerably longer to train.

Algorithms↗
PubMed2006

Assessing stability of gene selection in microarray data analysis.

BACKGROUND: The number of genes declared differentially expressed is a random variable and its variability can be assessed by resampling techniques. Another important stability indicator is the frequency with which a given gene is selected across subsamples. We have conducted studies to assess stability and some other properties of several gene selection procedures with biological and simulated data. RESULTS: Using resampling techniques we have found that some genes are selected much less frequently (across sub-samples) than other genes with the same adjusted p-values. The extent to which this type of instability manifests itself can be assessed by a method introduced in this paper. The effect of correlation between gene expression levels on the performance of multiple testing procedures is studied by computer simulations. CONCLUSION: Resampling represents a tool for reducing the set of initially selected genes to those with a sufficiently high selection frequency. Using resampling techniques it is also possible to assess variability of different performance indicators. Stability properties of several multiple testing procedures are described at length in the present paper.

Biomarkers, Tumor↗
PubMed1997

Sequence Data Analysis for Long Disordered Regions Prediction in the Calcineurin Family.

Our recently reported results (PSB 3:471-482, 1998; Proc. IEEE Intnl. Conf. Neural Networks 1:90-95, 1997; PSB 3:435-446, 1998) provide strong support for a hypothesis that some amino acid sequences code for disordered regions rather than structured ones and that such disordered regions are commonly involved in function. General and family-specific neural network predictors developed in those previous studies suggest that different classes of disordered regions exist. Here, family-specific data preprocessing for disorder prediction in the calcineurin (CaN) family is explored. The results show that prediction of order and disorder on CaN sequence data benefits significantly from the use of family-specific preprocessing, with feature extraction through principal components analysis (PCA) outperforming feature selection techniques, although all methods do a good job of discriminating CaN-specific disordered regions from CaN-specific ordered regions. On the other hand, for the discrimination of CaN-specific disordered regions from general (unrelated to CaN) ordered regions, feature selection approaches proved to be more appropriate than PCA. The results further support a hypothesis that different kinds of disordered regions exist, as all family-specific disorder predictors developed in this study significantly outperformed a previously reported general multi-family disorder predictor.

Journal Article↗
PubMed2005

High-throughput data analysis for detecting and identifying differences between samples in GC/MS-based metabolomic analyses.

In metabolomics, the objective is to identify differences in metabolite profiles between samples. A widely used tool in metabolomics investigations is gas chromatography-mass spectrometry (GC/MS). More than 400 compounds can be detected in a single analysis, if overlapping GC/MS peaks are deconvoluted. However, the deconvolution process is time-consuming and difficult to automate, and additional processing is needed in order to compare samples. Therefore, there is a need to improve and automate the data processing strategy for data generated in GC/MS-based metabolomics; if not, the processing step will be a major bottleneck for high-throughput analyses. Here we describe a new semiautomated strategy using a hierarchical multivariate curve resolution approach that processes all samples simultaneously. The presented strategy generates (after appropriate treatment, e.g., multivariate analysis) tables of all the detected metabolites that differ in relative concentrations between samples. The processing of 70 samples took similar time to that of the GC/TOFMS analyses of the samples. The strategy has been validated using two different sets of samples: a complex mixture of standard compounds and Arabidopsis samples.

Arabidopsis↗
PubMed2000

Thioridazine for dementia.

BACKGROUND: Neuroleptic drugs are controversial treatments in dementia, with evidence accumulating that they may hasten clinical decline. Despite these concerns, they are commonly prescribed for elderly and demented patients. Thioridazine, a phenothiazine neuroleptic, is one of the most commonly prescribed. It has often been a preferred agent because it is thought to produce relatively less frequent motor side effects. The drug has significant sedative effects, and it is thought that these are the main mechanism of action in calming and controlling the patient. However, pharmacologically, it also has marked anticholinergic properties that could potentially have a detrimental effect on cognitive function. OBJECTIVES: To determine the evidence on which the use of thioridazine in dementia is based in terms of: 1) efficacy in controlling symptoms 2) cognitive outcome for the patient 3) safety SEARCH STRATEGY: The Cochrane Controlled Trials Register and other electronic databases were searched using the terms 'thioridazine', 'melleril', 'dementia' and 'old age'. In addition, Novartis, the pharmaceutical company that developed and markets thioridazine, was approached and asked to release any published or unpublished data they had on file. SELECTION CRITERIA: Unconfounded, single-blind or double-blind, randomised trials were identified in which treatment with thioridazine was administered for more than one dose and compared to an alternative intervention in patients with dementia of any aetiology. Trials in which allocation to treatment or comparator were not truly random, or in which treatment allocation was not concealed were reviewed but are not included in the data analysis. DATA COLLECTION AND ANALYSIS: Data were extracted independently by the reviewers (VC, CAK and RJH). For continuous and ordinal variables, the main outcome measures of interest were the final assessment score and the change in score from baseline to the final assessment. The assessment scores were provided by behavioural rating scales, clinical global impression scales, functional assessment scales, psychometric test scores, and frequency and severity of adverse events. Data were pooled where appropriate or possible, and the Peto odds ratio (95%CI) or the weighted mean difference (95%CI) estimated. Where possible, intention to treat data were used. MAIN RESULTS: The meta-analysis showed that, compared with placebo, thioridazine reduced anxiety symptoms as evidenced by changes on the Hamilton Anxiety Scale. However, there was no significant effect on clinical global change, and a non-significant trend for higher adverse effects with thioridazine. Compared to diazepam, thioridazine was superior in terms of some anxiety symptoms, with similar adverse effects. Global clinical evaluation scales mostly did not favour either treatment. Compared to chlormethiazole, thioridazine was significantly inferior when assessed on some items of the CAPE and the Crichton Geriatric Behavioural Rating Scales. Thioridazine was also associated with significantly more dizziness. No superiority for thioridazine was shown in comparisons with etoperidone, loxapine or zuclopenthixol. REVIEWER'S CONCLUSIONS: Very limited data are available to support the use of thioridazine in the treatment of dementia. If thioridazine were not currently in widespread clinical use, there would be inadequate evidence to support its introduction. The only positive effect of thioridazine when compared to placebo is the reduction of anxiety. When compared to placebo, other neuroleptics, and other sedatives it has equal or higher rates of adverse effects. Clinicians should be aware that there is no evidence to support the use of thioridazine in dementia, and its use may expose patients to excess side effects.

Antipsychotic Agents↗
PubMed2001

Non-linear dynamics of cardiovascular system in humans exposed to repetitive apneas modeling obstructive sleep apnea: aggregated time series data analysis.

OBJECTIVE: Testing the hypothesis that alterations in non-linear dynamics of the cardiovascular variability appear in healthy, awake subjects during voluntary apnea. SUBJECTS AND METHODS: Ten young subjects performed 20 apneas 60 s each separated by 1 min free breathing. Inter-beat interval (IBI) measured as RR-interval in ECG, systolic (SYS) and diastolic (DIAS) arterial blood pressure. stroke volume (SV), cardiac output (CO) and total peripheral resistance (TPR) were non-invasively recorded and computed by Portapress 2 system. Correlation dimension according to Grassberger-Proccacia algorithm (CD) and ratio of % determinism versus % recurrence (RDR) computed from recurrence plot according to Webber and Zbiluth [J. Appl. Physiol. 76 (1994) 965] were used as the indices of chaos and complexity. Sequential time series of cardiovascular variables in consecutive 60-s apneas and inter-apnea free breathings were separately windowed and aggregated. CD and RDR of aggregated apneic time series were compared with CD and RDR values of aggregated time series of inter-apnea free breathing, 10 min at rest and 10 min recovery. Reliability of the aggregation method of sequential time series was tested on transformed simulated data generated by Lorenz model. Error in CD and RDR estimation did not exceed 5% and 1%. respectively. RESULTS: CD of cardiovascular variables computed from aggregated apneas was significantly reduced and RDR augmented versus control and recovery periods. CD and RDR values of inter-apnea phases were in between those in control and during apneas. Time domain linear variance (SD) was increased during aggregated apneas. CONCLUSIONS: Signal dynamics dependent windowing and data aggregation could be a useful tool for non-linear analysis of short repeatable sequential time series; time domain linear variability of the cardiovascular dynamics is augmented while complexity reduced during apneic chemoreceptor stimulation; alterations in non-linear dynamics of cardiovascular variables during apneas in healthy normotensive subjects may suggest an early sign of a mechanism implicated in arterial hypertension in OSAS.

Adult↗
PubMed2003

Fokker-Planck perspective on stochastic delay systems: exact solutions and data analysis of biological systems.

Stochastic delay systems with additive noise are examined from the perspective of Fokker-Planck equations. For a linear system, the exact stationary probability density is derived by means of a delay Fokker-Planck equation. We show how to determine the delay equation of the linear system from experimental data, and corroborate a fundamental result previously obtained by Küchler and Mensch. We also propose a method to derive delay equations of nonlinear systems from experimental data. To this end, the theory of multivariate Fokker-Planck equations is used. The applicability of this method is demonstrated for stochastic models describing tracking and pointing movements of humans.

Biophysical Phenomena↗
PubMed1980

Contrast media reactions: data analysis and hypothesis.

Two hundred and twenty-eight deaths due to the use of contrast media are reported, including 15 from intravenous cholangiography, 69 from angiography, 140 from urography and four other. The causes are analyzed and the various explanations for reactions to contrast media are considered. Data concerning the high incidence of cardiac death, the large number of deaths due to pulmonary edema, and the known transgression of the blood-brain barrier by contrast media are used to construct a theory that bases all reactions on the effect of contrast media on the central nervous system.

Adolescent↗