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At least 217 records · Page 12Linked to original sources

PubMed2003

Statistical methods for longitudinal research on bipolar disorders.

OBJECTIVES: Outcomes research in bipolar disorders, because of complex clinical variation over-time, offers demanding research design and statistical challenges. Longitudinal studies involving relatively large samples, with outcome measures obtained repeatedly over-time, are required. In this report, statistical methods appropriate for such research are reviewed. METHODS: Analytic methods appropriate for repeated measures data include: (i) endpoint analysis; (ii) endpoint analysis with last observation carried forward; (iii) summary statistic methods yielding one summary measure per subject; (iv) random effects and generalized estimating equation (GEE) regression modeling methods; and (v) time-to-event survival analyses. RESULTS: Use and limitations of these several methods are illustrated within a randomly selected (33%) subset of data obtained in two recently completed randomized, double blind studies on acute mania. Outcome measures obtained repeatedly over 3 or 4 weeks of blinded treatment in active drug and placebo sub-groups included change-from-baseline Young Mania Rating Scale (YMRS) scores (continuous measure) and achievement of a clinical response criterion (50% YMRS reduction). Four of the methods reviewed are especially suitable for use with these repeated measures data: (i) the summary statistic method; (ii) random/mixed effects modeling; (iii) GEE regression modeling; and (iv) survival analysis. CONCLUSIONS: Outcome studies in bipolar illness ideally should be longitudinal in orientation, obtain outcomes data frequently over extended times, and employ large study samples. Missing data problems can be expected, and data analytic methods must accommodate missingness.

Bipolar Disorder↗

PubMed2005

Chromatographic preprocessing of GC-MS data for analysis of complex chemical mixtures.

Hyphenated analytical techniques such as gas chromatography-mass spectrometry (GC-MS) can provide extensive amounts of analytical data when applied to environmental samples. Quantitative analyses of complex contaminant mixtures by commercial preprocessing software are time-consuming, and baseline distortion and incomplete peak resolution increase the uncertainty and subjectivity of peak quantification. Here, we present a semi-automatic method developed specific for processing complex first-order chromatographic data (e.g. selected ion monitoring in GC-MS) prior to chemometric data analysis. Chromatograms are converted into semi-quantitative variables (e.g. diagnostic ratios (DRs)) that can be exported directly to appropriate softwares. The method is based on automatic peak matching, initial parameterization, alternating background noise reduction and peak estimation using mathematical functions (Gaussian and exponential-Gaussian hybrid) with few (i.e. three to four) parameters. It is capable of resolving convoluted peaks, and the exponential-Gaussian hybrid improves the description of asymmetric peaks (i.e. fronting and tailing). The optimal data preprocessing suggested in this article consists of estimation of Gaussian peak parameters and subsequent calculation of diagnostic ratios from peak heights. We tested the method on chromatographic data from 20 replicate oil samples and found it to be less time-consuming and subjective than commercial software, and with comparable data quality.

Gas Chromatography-Mass Spectrometry↗

PubMed2000

Spirostanols obtained by cyclization of pseudosaponin derivatives and comparison of anti-platelet agglutination activities of spirostanol glycosides.

Naturally occurring saponins 3 and 4 have a normal type F ring and alpha-arranged CH(3)-21 group. Treatments of pseudosaponin peracetates 18 and 19 derived from 3 and 4, respectively, with alcoholic KOH, followed by acidification with acetic acid, gave spirostanols 20 and 22 having iso type F rings as major products. Structural analyses of sapogenins and saponins derived from pseudo derivatives 11, 12, 18 and 19 were performed by comparisons of their 1H-NMR spectral data and the X-ray analytical data of 3-O-p-bromobenzoyl sarsasapogenin 7, 3-O-acetyl diosgenin 13 and saponin 20. The mechanisms of ring-closure reaction of the side chain at C-22 of pseudosapogenins and pseudosaponins were deduced using stereomodels of the spirostanols derived from 11 under various reaction conditions. Inhibitory activities of saponin diglycosides 3, 4, 20, 21 and 25 on human platelet agglutinations induced by ADP and ristocetin were compared.

Adenosine Diphosphate↗

PubMed1997

Design of a study to improve accuracy in reading mammograms.

This paper is concerned with the design and analysis of mammography reading studies. In particular we consider studies aimed at evaluating interventions to improve the accuracy with which mammograms are read. A simple randomized design is suggested in which a relatively large group of readers read sets of mammograms before and after an intervention phase. We propose solutions to three difficult statistical issues that arise in the context of such studies: (i) the choice of primary outcome measure; (ii) the data analysis technique to be employed; and (iii) the methodology for calculating sample sizes for readers and images to be read. First, we argue in favor of using sensitivity and specificity as the primary outcome measures rather than receiver operating characteristic (ROC) curves in mammography studies, although the latter are considered state of the art for many types of radiology reading studies. We argue that sensitivity and specificity are more clinically relevant and conceptually more straightforward than ROC curves. Second, we suggest a bivariate approach to data analysis for evaluating intervention effects on sensitivity and specificity. This accommodates the correlations inherent between these measures and allows for estimation of joint effects on them. Finally we propose a method for power calculations that uses computer simulation techniques. Simple formulas for sample size calculations are not available in part because variability in accuracy amongst readers and variation in difficulty among images introduce complexity into power calculations. The simulation method that we propose accommodates such complexity and is easy to implement. The methodology was motivated by a study funded by the Department of Defense to evaluate the potential efficacy of an educational intervention. In the context of this study we illustrate the steps involved in power calculations and apply the data analytic techniques to the sort of data expected to result from this study. Though the proposed methods were motivated by this particular study, the statistical considerations are relevant more broadly in mammography and indeed in other types of radiologic imaging studies. Standards for the conduct of radiologic reading studies are not yet well developed, as they are for randomized clinical trials and for case-control studies. We hope that the discussion in this paper will add to the dialogue necessary for development of such standards.

Breast Neoplasms↗

PubMed2003

Pharmacokinetic and pharmacodynamic properties of insulin aspart and human insulin.

The preferred approach to determine the pharmacokinetic (PK) and pharmacodynamic (PD) properties of insulin analogues is the euglycemic glucose clamp. Currently non-compartmental data analytical approaches are used to analyze data. The purpose of the present study is to propose a novel compartmental-model for analysis of data from glucose clamp studies. Data used in this trial only involved 18 of the 20 originally treated subjects. Data was obtained from a crossover trial where 18 healthy subjects each received a single subcutaneous (s.c.) dose of 1.2 nmol/kg (body weight) insulin aspart (IAsp) or 1.2 nmol/kg human insulin (HI) during a euglycemic glucose clamp after overnight fast. Serum insulin and glucose concentrations were measured and the glucose infusion rate (GIR) was adjusted after dosing, to maintain blood glucose near basal levels. Individual model parameters were estimated for IAsp, HI, and the corresponding glucose and GIR data. We found statistically significant differences between most of the HI and IAsp pharmacokinetic parameters, including the sigmoidicity of the time course of absorption (1.5 for HI vs. 2.1 for IAsp (unit less), P = 0.0005, Wilcoxon Signed-rank test), elimination rate constant (0.010 min-1 for HI vs. 0.016 min-1 for IAsp (P = 0.002)). The PD model parameters were mostly not different, except for the rate of insulin action (0.012 min-1 for HI vs. 0.017 min-1 for IAsp (P = 0.03)). The model may provide a framework to account for different PK properties when estimating the PD properties of insulin and insulin analogues in glucose clamp experiments.

Adult↗

PubMed1992

EDMUS, a European database for multiple sclerosis.

EDMUS is a minimal descriptive record developed for research purposes to document clinical and laboratory data in patients with multiple sclerosis (MS). It has been designed by a committee of the European Concerted Action for MS, organised under the auspices of the Commission of the European Communities. The software is user-friendly and fast, with a minimal set of obligatory data. Priority has been given to analytical data and the system is capable of automatically generating data, such as diagnosis classification, using appropriate algorithms. This procedure saves time, ensures a uniform approach to individual cases and allows automatic updating of the classification whenever additional information becomes available. It is also compatible with future developments and requirements since new algorithms can be entered in the programme when necessary. This system is flexible and may be adapted to the users needs. It is run on Apple and IBM-PC personal microcomputers. Great care has been taken to preserve confidentiality of the data. It is anticipated that this "common" language will enable the collection of appropriate cases for specific purposes, including population-based studies of MS and will be particularly useful in projects where the collaboration of several centres is needed to recruit a critical number of patients.

Database Management Systems↗

PubMed2003

An Automated Peak Identification/Calibration Procedure for High-Dimensional Protein Measures From Mass Spectrometers.

Discovery of "signature" protein profiles that distinguish disease states (eg, malignant, benign, and normal) is a key step towards translating recent advancements in proteomic technologies into clinical utilities. Protein data generated from mass spectrometers are, however, large in size and have complex features due to complexities in both biological specimens and interfering biochemical/physical processes of the measurement procedure. Making sense out of such high-dimensional complex data is challenging and necessitates the use of a systematic data analytic strategy. We propose here a data processing strategy for two major issues in the analysis of such mass-spectrometry-generated proteomic data: (1) separation of protein "signals" from background "noise" in protein intensity measurements and (2) calibration of protein mass/charge measurements across samples. We illustrate the two issues and the utility of the proposed strategy using data from a prostate cancer biomarker discovery project as an example.

Journal Article↗

PubMedDate not supplied

Importance of analytical methods in pharmacokinetic and drug metabolism studies.

Pharmacokinetic and drug metabolism studies first request that good analytical data are available. The various methods that permit unchanged drugs and their metabolites to be separated, identified and quantitatively assayed are briefly reviewed. The present importance of gas chromatography/mass spectrometry is emphasized, as well as the limits of immunological assays. The sensitivity of the analytical assay has a direct impact on the validity of the pharmacokinetic model which is built up from plasma concentration data. The precision and accuracy of the assay is also critical, and it is not always easily estimated. A new significant parameter is the speed of analysis, and the resulting massive production of analytical data. New drugs coming from biotechnology, and new dosage forms, like targeted drugs, will create new analytical problems in the future. They will probably call for the development of new biological or pharmacological assay procedures, in addition to the physicochemical means of analysis.

Animals↗

PubMed1996

Standard reference materials and data quality assurance in the biomedical analysis of trace elements.

Accurate and precise analytical data of the concentrations of bio-analytes in bioclinical studies are of fundamental importance. Quality assurance procedures should always be performed to check the overall analytical work. This can be conveniently performed if appropriate standard reference materials with known concentrations of the analyte object of study are available. This paper underlines the key points related to the production and use of biological standard materials for trace element analysis. In particular, the present situation in the field of trace element determination in human biological fluids and the related problems are illustrated. The considerations given in this work may contribute to the preparation of the new biomarker standard materials.

Biomarkers↗

PubMed1997

[Differences in nutrient intake using different nutrient databases-- an example].

Mean dietary intake calculated from 25 7-day-food records by means of the three nutrient data bases modified Souci/Fachmann/Kraut (mSFK) 1986/87, extract of Bundeslebensmittelschlüssel (BLS) version 2.1, and extract of BLS version 2.2 revealed comparable results only for four of 27 nutrients considered. The greatest deviations were found for zink, fluoride, iodine, vitamin D, vitamin C, and dietary fiber. Comparing the revised BLS version 2.2 and mSFK, the differences in fluoride, iodine and dietary fiber intake data were markedly lower than found with the comparison of BLS 2.1 and mSFK; statistically significant differences no longer existed for the vitamins C and A (equivalents). As expected, using the mSFK data base with some missing fields for analytical data underestimation of nutrient intake could be shown for the trace elements zink, fluoride and iodine. With regard to the given results of the investigated group, care has to be taken with some nutrient intake data gathered by means of BLS 2.1, too.

Diet Records↗

PubMed2004

Retrieval of missing data for meta-analysis: a practical example.

OBJECTIVES: To examine the feasibility of retrieving missing outcome data for summary meta-analyses using an example dealing with the effects of aerobic exercise on lipids and lipoproteins in adults. METHODS: Missing lipid and/or lipoprotein data from a currently developed meta-analytic data base were requested by means of electronic mail from 39 of 174 (22.4 percent) eligible studies. Binary logistic regression was used to examine whether year of publication and country were significant predictors for whether data would be provided. RESULTS: Of the thirty-nine studies from which data were requested, usable data were received for thirteen (33.3 percent) of the studies. The addition of these previously missing data decreased the percentage of eligible studies that would have had to be excluded by 33.5 percent (from 22.4 percent to 14.9 percent). Neither year of publication nor country in which the study was conducted (United States versus other) were significant predictors of whether missing data would be provided or not (p > .05). CONCLUSIONS: Moderate success was achieved in the acquisition of missing outcome data dealing with the effects of aerobic exercise on lipids and lipoproteins in adults. However, whether this level of response is true in other areas of research needs to be determined by additional research.

Clinical Trials as Topic↗

PubMed1999

The German Food Code and Nutrient Data Base (BLS II.2).

This article describes the conception and structure of the German Food Code and Nutrient Data Base (BLS). The data bank contains approx. 12,000 coded foods, menus and menu components in different stages of processing with up to 158 nutritional data for each product. Since comparatively few analytical data on the composition of foods are available, the majority of the data in the BLS are based on nutritional data calculated from recipes. Thus, a standard instrument for an uninterrupted (no missing values) evaluation of consumption surveys is made available.

Databases as Topic↗

PubMed1990

Individual-differences assessment of the relationship between change in and initial level of adult cognitive functioning.

Methodological factors may have been partially responsible for the inconsistency in findings from previous investigations into the relationship between change in, and initial level of, adult cognitive functioning. An alternative data-analytic procedure is proposed and applied to data from 277 men (25-76 years of age at initial testing) over 3 measurement occasions (interwave intervals of 6.7 years). Performances on both the Benton Revised Visual Retention Test (BVRT) and the Wechsler Adult Intelligence Scale (WAIS) Vocabulary subtest were analyzed. The findings demonstrate that the significant negative relationships between change and initial status, found on both tests, were partially a function of measurement error. Once adjustments were made for errors of measurement, the previously significant negative relationship for the BVRT data became significantly positive, whereas for the WAIS the relationship remained significantly negative, although to a lesser degree. The importance of accounting for errors of measurement is discussed.

Adult↗

PubMed1998

The use of stable isotope labeling and liquid chromatography-tandem mass spectrometry techniques to simultaneously determine the oral and ophthalmic bioavailability of timolol in dogs.

Assays have been established for the quantitation of timolol and its 13C3- and 2H9-stable-isotope-labeled analogs in plasma and urine using liquid chromatography with atmospheric-pressure chemical-ionization tandem mass spectrometry. For the analysis of urine, underivatized timolol and its labeled analogs are monitored while timolol in plasma is assayed down to concentrations of 0.2 ng/mL after derivatization with phosgene. The great power of this technique is illustrated by simultaneously assaying three different species of timolol in plasma and urine obtained from dogs receiving simultaneous ophthalmic, oral, and intravenous doses of unlabeled and [2H9]- and [13C3]-labeled timolol. Thus, the ophthalmic and oral bioavailabilities of timolol are measured in a single experiment rather than as a three-phase crossover experiment. This approach yields accurate and precise analytical data, obviates intrasubject variability, and saves both analytical and animal resources.

Administration, Oral↗

PubMed1985

Synthesis of peptide labelled with p-iodophenylalanine which corresponds to the first amphipathic region of apolipoprotein C-I.

The amino terminal fragment (1-15) of apolipoprotein C-1, H-Thr-Pro-Asp-Val-Ser-Ser-Ala-Leu-Asp-Lys-Leu-Lys-Glu-Phe14-Gly was prepared by the solid phase method. However, the phenylalanine residue at position 14 was replaced with p-iodophenylalanine in the chemical synthesis. The preparation of t-butyloxy-carbonyl-p-iodophenylalanine is described. After completion of the synthesis, the product was deprotected and cleaved from the resin with liquid HF. The peptide was purified by gel filtration on Sephadex G-25 and preparative high performance liquid chromatography. The purified material was shown to be homogeneous by amino acid analytical data and by chromatography in three different analytical reversed phase HPLC systems. The peptide was then labelled by the chloroamine-T procedure and good incorporation of 125I was obtained. After purification of the product by gel filtration on Biogel P-2, the labelled pentadecapeptide was tested for ability to bind to Very Low Density Lipoproteins (VLDL) in the following manner: VLDL was isolated from normolipemic serum by ultracentrifugal flotation and 100-microliter samples were incubated with labelled material dissolved in 200 microliter of 0.5 M NaCl, 0.02 M sodium phosphate buffer, pH 7.4 at 37 degrees for 30 min. The VLDL fraction was again isolated by ultracentrifugal flotation and the incorporation of radioactivity into the lipoprotein was measured. Under these conditions, a sample of [3H]-native apolipoprotein C-I was incorporated to an extent of 83% of the total sample, while the [125I]-pentadecapeptide exhibited an incorporation of 8.7%.

Amino Acid Sequence↗

PubMed1989

Receiver operating characteristic (ROC) methodology: the state of the art.

Receiver operating characteristic (ROC) methodology has been increasingly used in medical applications in the last 10 years. The text by Swets and Pickett has popularized the technique and the journal Medical Decision Making (1981--) provides a forum for further methodologic issues. In this article, I will (1) describe the nature of the data generated by ROC studies; (2) evaluate the choices of summary indices of performance (accuracy); (3) outline the data-analytic techniques used, and how to incorporate data from multiple observers and multiple "readings"; (4) review proposed alternatives to the commonly used binormal ROC model; and (5) discuss issues, such as verification bias, and challenges, such as multicenter comparative imaging studies and the difficulty of obtaining "truth data", which need to be addressed when adapting ROC methods to medical contexts.

ROC Curve↗

PubMed1994

[Malignant tumors of the Vater's ampulla. Presentation of 28 cases and review of the literature].

We present a study of 28 patients, treated for adenocarcinoma of Vater's ampulla. We emphasize the distinct behavior of each one of the peri-ampullar tumors, those which affect Vater's ampulla yielding the best prognosis. We gathered data regarding gender, age, clinical manifestations, and analytical data. The confirmatory diagnosis gives us 100% of CPRE cases. All of the patients were submitted to surgical treatment with anatomic pathological confirmation of the diagnosis, be it pre or postoperative. We practiced curative surgery in 57.2% of the cases and palliative in 42.8% of the cases. We observed postoperative complications in 17.8% of the patients and peroperative mortality in 3.5%. Actual survival of the series of patients for whom exeretic surgery was performed is significantly superior to that of the other patients.

Actuarial Analysis↗

PubMedDate not supplied

Organization and education in occupational safety and health in Maghreb countries.

The Maghreb consists of five countries of North Africa (Mauritania, Morocco, Algeria, Tunisia and Libya) which are members of a socio-economical community called the Union of Arab Maghreb. This paper discusses the organisation of occupational health, medical protection of workers and training in occupational safety and health in these countries. After a review of socio-economic and demographic data and legislative aspects, we report epidemiological and analytic data specific to each country concerning organisation and training in occupational health. Occupational medicine in Algeria, Morocco and Tunisia has progressed but some deficiencies are still observed at several levels. Like countries of the European Union, cooperation between the Maghreb countries in occupational health and safety seems indispensable.

Africa, Northern↗