Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “STATISTICS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,369 records · Page 76Linked to original sources
PubMed1998

Statistical features of human exons and their flanking regions.

To facilitate gene finding and for the investigation of human molecular genetics on a genome scale, we present a comprehensive survey on various statistical features of human exons. We first show that human exons with flanking genomic DNA sequences can be classified into 12 mutually exclusive categories. This classification could serve as a standard for future studies so that direct comparisons of results can be made. A database for eight categories (related to human genes in which coding regions are split by introns) was built from GenBank release 87.0 and analyzed by a number of methods to characterize statistical features of these sequences that may serve as controls or regulatory signals for gene expression. The statistical information compiled includes profiles of signals for transcription, splicing and translation, various compositional statistics and size distributions. Further analyses reveal novel correlations and constraints among different splicing features across an internal exon that are consistent with the Exon Definition model. This information is fundamental for a quantitative view of human gene organization, and should be invaluable for individual scientists to design human molecular genetics experiments.

Adenine↗
PubMed1993

Impact of different statistical methodologies on the evaluation of the in-vitro MICs for Bacteroides fragilis of selected cephalosporins and cephamycins.

The purpose of this study was to assess the effect of different MIC statistics on the in-vitro evaluation of cefoxitin, cefotetan, ceftizoxime, cefotaxime, desacetylcefotaxime, and cefotaxime:desacetylcefotaxime (1:1 ratio) against clinical isolates of Bacteroides fragilis from the Medical University of South Carolina. MICs were determined by the agar dilution method following NCCLS guidelines. Statistical analyses included arithmetic and geometric means, median, mode, MIC50, MIC90, and range. Differences between antimicrobial agents were determined using parametric and nonparametric methods. Consistent with previous in-vitro studies on anaerobes with these agents, a wide range in the MICs was observed. The arithmetic mean MIC was lowest for cefotetan, but the geometric mean MIC was lowest for ceftizoxime. Using the MIC90, cefotetan was at least a two-fold dilution more active than the other agents. After natural logarithmic transformation of the MIC data, analysis of variance with the Scheffé post-hoc test demonstrated that the MICs of ceftizoxime were significantly lower than those of cefoxitin (P < 0.001), cefotetan (P < 0.05), cefotaxime (P < 0.05), and desacetylcefotaxime (P < 0.001). Median and mode MICs were lowest for ceftizoxime and cefotaxime:desacetylcefotaxime. Using published breakpoints, cumulative percent susceptibility was similar for all agents studied. In this analysis of the antimicrobial susceptibility of B. fragilis in our institution, the in-vitro activity of the cephalosporins and cephamycins tested appeared to be very similar when all statistical data were evaluated. Since apparent in-vitro activity may be influenced by the statistic evaluated, we suggest that all MIC data be reported to allow for a more complete analysis of microbiological potency.

Analysis of Variance↗
PubMed2005

A statistical approach based on substitution of macronutrients provides additional information to models analyzing single dietary factors in relation to type 2 diabetes in danish adults: the Inter99 study.

Most studies analyzing diet-disease relations focus on single dietary factors rather than combining different nutrients into the same statistical model. The objective of this study was to identify dietary factors associated with the probability of having diabetes identified by screening (SDM) in Danish men and women aged 30-60 y. A specific objective was to examine whether an alternative statistical approach could provide additional information to already existing statistical approaches used in nutritional epidemiology. Baseline data from the Danish population-based Inter99 study were used. The dietary intake of 262 individuals with SDM was compared with that of 4627 individuals with normal glucose tolerance (NGT) using 2 different types of multiple logistic regression models adjusted for potential confounders. The first model included single dietary factors, whereas the second model was based on substitution of macronutrients. In the models with single dietary factors, high intakes of carbohydrates, dietary fiber, and coffee were inversely associated with SDM (P < 0.01), whereas high intakes of total fat and saturated fat were positively associated with SDM (P < 0.05). A modest U-shaped association was found between alcohol consumption and SDM (P = 0.10) [corrected] Results from the substitution model showed that when 3% of energy (En%) as carbohydrate replaced 3 En% fat or alcohol, the probability of having SDM decreased by 9 and 10%, respectively (P < 0.01) [corrected] No other macronutrient substitutions resulted in significant associations. Hence, the statistical approach based on substitution of macronutrients provided additional information to the model analyzing single dietary factors.

Adult↗
PubMed2003

Statistics of the Comet assay: a key to discriminate between genotoxic effects.

The alkaline Comet assay is a widely used single cell gel electrophoresis technique for the quantification of DNA strand breaks, crosslinks and alkali-labile sites induced by a series of physical and chemical agents. DNA migration in an electric field, supposed proportional to strand breakage, is a proposed estimation of genotoxicity. Breaks are quantified from geometric and fluorescence measurements by image analysis of comet-shaped DNA, often reported parameters being tail DNA and tail moment. Although a variety of statistical approaches have been used in the literature, most of these do not take into account the distribution patterns of comet data. In order to investigate a methodology for statistically demonstrating a comet effect, two different experiments, a reproducibility study and a trend analysis, were undertaken on a murine lymphoma cell line (P388D1) photodynamically stressed after induction of porphyrins with delta-aminolaevulinic acid. This treatment results in significant heterogeneity of DNA damage, producing values ranging from 0 to 100% tail DNA in the same sample. The comparison of distribution curves for stressed and non-stressed samples shows that none of the application conditions are verified, either for parametric tests (which require normal distributions), or non-parametric tests (which assume essentially similar distributions). Meaningful statistics (median and 75th percentile) were consequently extracted from repeated experiments and found suitable for comparing stress conditions in an ANOVA and in a trend analysis; the 75th percentile is theoretically more sensitive but tends to more rapidly saturate at extensive stress levels. We conclude that a trend analysis of median comet metrics from repeated experiments at different stress levels is certainly an efficient way to statistically demonstrate a genotoxic effect. Whether the considered comet parameter is tail DNA or tail moment had no influence on the conclusions of our experiments, which were carried up to stress levels leading to a median 70% tail DNA.

Aminolevulinic Acid↗
PubMed2004

A study of mortality patterns at a tyre factory 1951-1985: a reference statistic dilemma.

BACKGROUND: The general and cancer mortalities of rubber workers at a large tyre factory were studied in an area of marked regional variation in death rates. METHODS: Three quinquennial intakes of male rubber workers engaged between January 1946 and December 1960 formed a composite cohort of 6454 men to be followed up. Over 99% were successfully traced by December 1985. The cohort analysis used both national and local rates as reference statistics for several causes. RESULTS: Between 1951 and 1985, a national standardized mortality ratio (SMRN) of 101 for all causes (based on 2556 deaths) was noted, whereas the local standardized mortality ratio (SMRL) was only 79. For all cancers, the figures were 115 (SMRN) and 93 (SMRL), for stomach cancer they were 137 (SMRN) and 84 (SMRL), and for lung cancer they were 121 (SMRN) and 94 (SMRL). No outright excesses against the national norm were observed for other cancers except for larynx, brain and central nervous system and thyroid cancer and the leukaemias. Excesses were statistically significant for cancer of the gallbladder and the bile ducts, for silicotuberculosis (SMRN = 1000) and for the pneumoconioses (SMRN = 706). Deaths from cerebrovascular diseases, chronic bronchitis and emphysema showed statistically significant deficits using either norm. CONCLUSIONS: These results from a large factory cohort study of rubber workers, followed for over three decades, demonstrate the marked discrepancy that can result from using only one reference statistic in areas of significant variation in mortality patterns.

Aged↗
PubMed1985

The phylogeny of the hominoid primates: a statistical analysis of the DNA-DNA hybridization data.

Sibley and Ahlquist compared the single-copy nuclear DNA sequences of the hominoid primates using DNA-DNA hybridization. From this data set they estimated a phylogeny that clusters man and chimpanzees using a distance Wagner procedure. However, no assessment of statistical confidence in this estimated phylogeny was made, despite the fact that their data set contains internal inconsistencies concerning the correct branching order. This paper presents a modification of Pielou's Q-statistic that allows one to make nonparametric tests of phylogenetic relationship from distance data. The results of this analysis indicate that the estimated phylogeny of Sibley and Ahlquist is without statistical significance owing to the internal inconsistencies of the data set. A survey and additional analyses of other types of molecular data indicate that the phylogeny that clusters chimpanzees and gorillas and has the human lineage splitting off earlier is statistically consistent with all the molecular data (including the DNA-DNA hybridization data), whereas the phylogeny estimated by Sibley and Ahlquist can be rejected at the 5% level using the data on restriction-endonuclease sites in the mitochondrial genome.

Animals↗
PubMed1983

Multivariate statistics and meaning in the study of psychopathology.

A recent article dealing with Schneiderian first-rank symptoms illustrates a frequent occurrence: the use of sophisticated statistical data analysis without clear concepts of either psychopathology or statistics. The purpose of this article is to present some guidelines for the interpretation of multivariate statistics and to increase sensitivity to the importance of integrating underlying clinical concepts with statistical data analysis.

Humans↗
PubMed1995

Defining quality of perioperative care by statistical process control of adverse outcomes.

BACKGROUND: Through peer review, we separated the contributions of system error and human (anesthesiologist) error to adverse perioperative outcomes. In addition, we monitored the quality of our perioperative care by statistically defining a predictable rate of adverse outcome dependent on the system in which practice occurs and respondent to any special causes for variation. METHODS: Traditional methods of identifying human errors using peer review were expanded to allow identification of system errors in cases involving one or more of the anesthesia clinical indicators recommended in 1992 by the Joint Commission on Accreditation of Healthcare Organizations. Outcome data also were subjected to statistical process control analysis, an industrial method that uses control charts to monitor product quality and variation. RESULTS: Of 13,389 anesthetics, 110 involved one or more clinical indicators of the Joint Commission on Accreditation of Healthcare Organizations. Peer review revealed that 6 of 110 cases involved two separate errors. Of these 116 errors, 9 (7.8%) were human errors and 107 (92.2%) were system errors. Attribute control charts demonstrated all indicators, excepting one (fulminant pulmonary edema), to be in statistical control. CONCLUSIONS: The major determinant of our patient care quality is the system through which services are delivered and not the individual anesthesia care provider. Outcome of anesthesia services and perioperative care is in statistical control and therefore stable. A stable system has a measurable, communicable capability that allows description and prediction of the quality of care we provide on a monthly basis.

Aftercare↗
PubMed1995

A systematic approach to conducting a non-statistical meta-analysis of research literature.

Literature analyses and syntheses are becoming increasingly important as a means of periodically bringing coherence to a research area, contributing new knowledge revealed by integrating single studies, and quickly informing scientists of the state of the field. As a result, there is a need for approaches that can provide replicable, reliable, and trustworthy results. Over the last decade many researchers have begun using the statistical meta-analysis approach to integrate studies. However, the single studies conducted in many areas are not of the type amenable to statistical meta-analysis but are more appropriate for non-statistical analysis and synthesis. The present paper describes (1) a rigorous approach to conducting a non-statistical meta-analysis of research literature and (2) an example of how this approach was applied to the literature of determinants of primary care specialty choice published between 1987 and 1993. This approach includes model development, literature retrieval, literature coding, rating references for quality, annotating high-quality references, and synthesizing only the subset of the literature found of sufficient quality to be considered. Also, the basic results of each included study are reported in the synthesis so that readers have before them all the "data points" used in the synthesis. Thus, readers can draw their own interpretations without having to re-collect the data, just as they would be able to do in any single study that presents original data as well as conclusions and discussion.

Meta-Analysis as Topic↗
PubMed2003

Statistical validation of a commonly used method for personnel dosimetry issuance determinations.

In 1992, the federal requirements for personnel monitoring of occupational radiation doses were modified, making monitoring compulsory only for individuals "likely" to exceed 10% of the applicable annual dose limits. This regulatory change served as a catalyst for many radiation protection programs to re-evaluate their personnel monitoring issuance criteria to determine if some monitoring services might be reduced or eliminated. But in the absence of any clear definition of the term "likely," radiation protection programs relied on adjustments largely based on reviews of previous monitoring results and professional judgment. Although such semi-quantitative assessments may have been appropriate, the approach was not without inherent programmatic risks, as radiation dosimetry programs have been shown to be a consistent source of regulatory non-compliance upon inspection and serve as essential elements in defense against litigation efforts purporting workplace-related radiation injury. The objective of this study was to subject this commonly used method for post-regulatory change dosimetry issuance determinations to statistical validation. Personnel monitoring data from The University of Texas Health Science Center at Houston Radiation Safety Program pre- and post-1992 regulatory changes were accessed and descriptively analyzed. The dynamic nature of the institutional environment made direct comparisons of individuals between years impractical, so 1990 mean dose levels for various independent variables were compared using the Kruskal-Wallis non-parametric ANOVA test at a significance level of alpha = 0.05. The data from 1998 were then analyzed to ascertain if the groupings identified as statistically different in 1990 were still being monitored. The analyses statistically validated the monitoring program reductions made by the University of Texas Health Science Center at Houston radiation protection program. In addition, statistical support for further monitoring program reductions were identified, if such reductions were deemed to be necessary in the future.

Government Agencies↗
PubMed1996

Recording, notification, compilation, and classification of statistics of occupational accidents and diseases: the Thai experience.

An International Labour Organization (ILO) project was conducted in July and August 1995 in Thailand to assist with the development of an information system on occupational accidents and diseases for the Workmen's Compensation Fund (WCF). The WCF provides cash benefits and medical care to insured workers who suffer employment injuries. The project included literature research based on the facilities of the ILO in Bangkok, and those of the Thai government, and a thorough review of the ILO Code of Practice (the Code) on recording and notification of occupational accidents and diseases, and of other international recommendations on statistics of occupational accidents and diseases. A comparative study of various notification systems of occupational accidents and diseases in Australia, Canada, the Philippines, Sweden, Thailand, and the United States was conducted. The project also included fact-finding sessions among various information suppliers and users in Thailand. The Thai notification form for collecting data for the database was redesigned and pretested. Results of the project indicated that the Code is appropriate for the recording and notification of occupational accidents and diseases in Thailand. In addition, a number of information requirements, which were included in the notification systems in the countries studied but not listed in the Code, were found to be useful for the database. A list of the baseline variables to be included in the proposed database was developed, the notification form was redesigned, and coding schemes for the information collected on the redesigned form were constructed on the basis of international standard classification systems for economic activity, employment status, occupation, nature of injury, occupational disease, body part, type of accident, and agency. A number of mechanisms were suggested for cross-checking the accuracy of data in the database. Based on the review of the Code and other international recommendations on statistical reporting, a list of baseline statistics was formulated for inclusion in the WCF annual report. Lastly, some suggestions for future statistical analysis of the database were given.

Accidents, Occupational↗
PubMed2003

Methodological and statistical considerations in measuring alcohol treatment effects.

This article addresses the design and selection of outcome methods for treatment research from a statistical perspective. Two of the major statistical and methodological issues relevant to the selection of dependent variable(s) are statistical power and social utility. Power is the paramount issue in research design. Power can be improved by measures and methods tailored to the predicted effects of treatment. These effects should vary from treatment to treatment, suggesting that no single outcome measure is suitable for all purposes. In estimating power, researchers should also consider the time-varying nature of most types of treatment effects. Given these considerations, timeline procedures have advantages because they allow the derivation of measures linked to specific treatment components. They also permit the study of time-varying effects of variables such as life stress. An analysis on the relationship between drinking and self-reported stress is presented as an illustration of how advanced statistical methods, in conjunction with carefully gathered data, can provide process data on how treatment can affect individual responses to stressors or other events. From a social utility perspective, however, having research focus on narrower and narrower slices of behavior in the search for power raises questions about the value of this research to clients and society. For dealing with this dilemma, it will be necessary to build a series of studies linking improvement in specific aspects of short-term outcome to longer term outcome and ultimately benefit to society.

Alcoholism↗
PubMed2006

Farm Scale Evaluations of spring-sown genetically modified herbicide-tolerant crops: a statistical assessment.

Primary results from the Farm Scale Evaluations (FSEs) of spring-sown genetically modified herbicide-tolerant crops were published in 2003. We provide a statistical assessment of the results for count data, addressing issues of sample size (n), efficiency, power, statistical significance, variability and model selection. Treatment effects were consistent between rare and abundant species. Coefficients of variation averaged 73% but varied widely. High variability in vegetation indicators was usually offset by large n and treatment effects, whilst invertebrate indicators often had smaller n and lower variability; overall, achieved power was broadly consistent across indicators. Inferences about treatment effects were robust to model misspecification, justifying the statistical model adopted. As expected, increases in n would improve detectability of effects whilst, for example, halving n would have resulted in a loss of significant results of about the same order. 40% of the 531 published analyses had greater than 80% power to detect a 1.5-fold effect; reducing n by one-third would most likely halve the number of analyses meeting this criterion. Overall, the data collected vindicated the initial statistical power analysis and the planned replication. The FSEs provide a valuable database of variability and estimates of power under various sample size scenarios to aid planning of more efficient future studies.

Agriculture↗
PubMed2003

Bayesian computation: a statistical revolution.

The 1990s saw a statistical revolution sparked predominantly by the phenomenal advances in computing technology from the early 1980s onwards. These advances enabled the development of powerful new computational tools, which reignited interest in a philosophy of statistics that had lain almost dormant since the turn of the century. In this paper we briefly review the historic and philosophical foundations of the two schools of statistical thought, before examining the implications of the reascendance of the Bayesian paradigm for both current and future statistical practice.

Journal Article↗
PubMed1999

Statistical-mechanical predictions and Navier-Stokes dynamics of two-dimensional flows on a bounded domain.

In this paper the applicability of a statistical-mechanical theory to freely decaying two-dimensional (2D) turbulence on a bounded domain is investigated. We consider an ensemble of direct numerical simulations in a square box with stress-free boundaries, with a Reynolds number that is of the same order as in experiments on 2D decaying Navier-Stokes turbulence. The results of these simulations are compared with the corresponding statistical equilibria, calculated from different stages of the evolution. It is shown that the statistical equilibria calculated from early times of the Navier-Stokes evolution do not correspond to the dynamical quasistationary states. At best, the global topological structure is correctly predicted from a relatively late time in the Navier-Stokes evolution, when the quasistationary state has almost been reached. This failure of the (basically inviscid) statistical-mechanical theory is related to viscous dissipation and net leakage of vorticity in the Navier-Stokes dynamics at moderate values of the Reynolds number.

Journal Article↗
PubMed2000

Constrained systems and statistical distribution

Theoretical advances in the statistical description of non-Hamiltonian systems [Tuckerman, Mundy, and Martyna, Europhys. Lett. 45, 149 (1999)] have recently led us to rethink the definition of the phase-space probability by using the proper invariant measure. Starting from this point of view, we will derive the statistical distribution of constrained systems, considered as non-Hamiltonian, in Cartesian coordinates, in a way independent from the standard Lagrangian treatment. Furthermore, we will analyze the statistical distribution of the Nose-Hoover isothermal (canonical or NVT) dynamics, considering with care the conservation laws hidden in the evolution equations. Consequently, we will correct the equations of motion in order to obtain the proper statistical ensemble. The isobaric-isothermal (constant pressure or NpT) form of the Nose-Hoover dynamics is then considered as a nontrivial extension of the described procedure and, similarly to the NVT case, we will correct the equations of motion with respect to previous versions. The case of a constrained system coupled to a thermostat and a piston is easily handled by means of the same formalism, whereas the Lagrangian treatment becomes involved.

Journal Article↗
PubMed2002

Temperature statistics in two-dimensional stably stratified turbulence.

Using two-dimensional direct numerical simulations, the statistics of temperature differences in stably stratified turbulence are studied. Comparison with passive scalar statistics in similar flows suggests that the stably stratified case is qualitatively similar to the passive case. Probability distribution functions of temperature differences between points separated by different distances collapse using the same scalings in both passive scalar and stably stratified simulations. Some dependence on stratification strength is evident, but the qualitative similarity may be due to the dominance of the large-scale flow in determining the temperature statistics. We also explore the stratification dependence of the statistics of temperature values and gradients.

Journal Article↗
PubMed2002

Combinatorial interpretation of Haldane-Wu fractional exclusion statistics.

Assuming that the maximal allowed number of identical particles in a state is an integer parameter, q, we derive the statistical weight and analyze the associated equation that defines the statistical distribution. The derived distribution covers Fermi-Dirac and Bose-Einstein ones in the particular cases q=1 and q--> infinity (n(i)/q-->1), respectively. We show that the derived statistical weight provides a natural combinatorial interpretation of Haldane-Wu fractional exclusion statistics, and present exact solutions of the distribution equation.

Journal Article↗