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 1,063 records · Page 59Linked to original sources
PubMed2006

What influences the choice of assessment methods in health technology assessments? Statistical analysis of international health technology assessments from 1989 to 2002.

OBJECTIVES: Health technology assessment (HTA) has been used as input in decision making worldwide for more than 25 years. However, no uniform definition of HTA or agreement on assessment methods exists, leaving open the question of what influences the choice of assessment methods in HTAs. The objective of this study is to analyze statistically a possible relationship between methods of assessment used in practical HTAs, type of assessed technology, type of assessors, and year of publication. METHODS: A sample of 433 HTAs published by eleven leading institutions or agencies in nine countries was reviewed and analyzed by multiple logistic regression. RESULTS: The study shows that outsourcing of HTA reports to external partners is associated with a higher likelihood of using assessment methods, such as meta-analysis, surveys, economic evaluations, and randomized controlled trials; and with a lower likelihood of using assessment methods, such as literature reviews and "other methods". The year of publication was statistically related to the inclusion of economic evaluations and shows a decreasing likelihood during the year span. The type of assessed technology was related to economic evaluations with a decreasing likelihood, to surveys, and to "other methods" with a decreasing likelihood when pharmaceuticals were the assessed type of technology. CONCLUSIONS: During the period from 1989 to 2002, no major developments in assessment methods used in practical HTAs were shown statistically in a sample of 433 HTAs worldwide. Outsourcing to external assessors has a statistically significant influence on choice of assessment methods.

Choice Behavior↗
PubMedDate not supplied

Predictive toxicology: benchmarking molecular descriptors and statistical methods.

The development of drugs depends on finding compounds that have beneficial effects with a minimum of toxic effects. The measurement of toxic effects is typically time-consuming and expensive, so there is a need to be able to predict toxic effects from the compound structure. Predicting toxic effects is expected to be challenging because there are usually multiple toxic mechanisms involved. In this paper, combinations of different chemical descriptors and popular statistical methods were applied to the problem of predictive toxicology. Four data sets were collected and cleaned, and four different sets of chemical descriptors were calculated for the compounds in each of the four data sets. Three statistical methods (recursive partitioning, neural networks, and partial least squares) were used to attempt to link chemical descriptors to the response. Good predictions were achieved in the two smaller data sets; we found for large data sets that the results were less effective, indicating that new chemical descriptors or statistical methods are needed. All of the methods and descriptors worked to a degree, but our work hints that certain descriptors work better with specific statistical methods so there is a need for better understanding and for continued methods development.

Drug Design↗
PubMed2005

Protein NMR recall, precision, and F-measure scores (RPF scores): structure quality assessment measures based on information retrieval statistics.

One of the most important challenges in modern protein NMR is the development of fast and sensitive structure quality assessment measures that can be used to evaluate the "goodness-of-fit" of the 3D structure with NOESY data, to indicate the correctness of the fold and accuracy of the resulting structure. Quality assessment is especially critical for automated NOESY interpretation and structure determination approaches. This paper describes new NMR quality assessment scores, including Recall, Precision, and F-measure scores (referred to here are "NMR RPF" scores), which quickly provide global measures of the goodness-of-fit of the 3D structures with NOESY peak lists using methods from information retrieval statistics. The sensitivity of the F-measure is improved using a scaled Fold Discriminating Power (DP) score. These statistical RPF scores are quite rapid to compute since NOE assignments and complete relaxation matrix calculations are not required. A graphical method for site-specific assessment of structure quality based on the Precision statistic is also described. These statistical measures are demonstrated to be valuable for assessing protein NMR structure accuracy. Their relationships to other proposed NMR "R-factors" and structure quality assessment scores are also discussed.

Databases, Protein↗
PubMed1998

Theoretical calculation and prediction of brain-blood partitioning of organic solutes using MolSurf parametrization and PLS statistics.

Sixty-three structurally diverse compounds were investigated to statistically model the brain-blood partitioning of organic solutes using theoretically computed molecular descriptors and multivariate statistics. The program MolSurf was used to compute theoretical molecular descriptors related to physicochemical properties such as lipophilicity, polarity, polarizability, and hydrogen bonding. The multivariate Partial Least Squares Projections to Latent Structures (PLS) method was used to delineate the relationship between the brain-blood partitioning of organic solutes and the theoretically computed molecular descriptors. Good statistical models were derived. Properties associated with polarity and Lewis base strength had the largest impact on the blood-brain partitioning and should be kept to a minimum to promote high partitioning. The absence of atoms capable of hydrogen bonding interactions as well as high lipophilicity and the presence of polarizable surface electrons, i.e., valence electrons, were also found to promote high brain-blood partitioning. The results indicate that theoretically computed molecular MolSurf descriptors in conjunction with multivariate statistics of PLS type can be used to successfully model the brain-blood partitioning of organic solutes and hence differentiate drugs with poor partitioning from those with acceptable partitioning at an early stage of the preclinical drug-discovery process.

Blood-Brain Barrier↗
PubMed1997

Theoretical calculation and prediction of Caco-2 cell permeability using MolSurf parametrization and PLS statistics.

PURPOSE: To statistically model the permeability across Caco-2 cell monolayers using theoretically computed molecular descriptors and multivariate statistics. METHODS: Seventeen structurally diverse compounds were investigated. The program MolSurf was used to compute theoretical molecular descriptors related to physico-chemical properties such as lipophilicity, polarity, polarizability and hydrogen bonding. The multivariate Partial Least Squares Projections to Latent Structures (PLS) method was used to delineate the relationship between the permeability across Caco-2 cell monolayers and the theoretically computed molecular descriptors. RESULTS: Excellent statistical models were derived. Properties associated with hydrogen bonding had the largest impact on diffusion through the monolayers and should be kept at a minimum to promote high permeability. High lipophilicity and the presence of surface electrons, i.e. valence electrons, which are not tightly bonded to the molecule, were also found to have a favorable influence to achieve high permeability. CONCLUSIONS: The results indicate that theoretically computed molecular MolSurf descriptors in conjunction with multivariate statistics of PLS type can be used to successfully model permeability across Caco-2 cell monolayers and, thus, differentiate drugs with poor permeability from those with acceptable permeability at an early stage of the preclinical drug discovery process.

Caco-2 Cells↗
PubMed1996

In-vitro dissolution profile comparison: statistics and analysis, model dependent approach.

PURPOSE: To develop and propose a "model dependent' approach for the in-vitro dissolution profiles comparison. METHODS: Diltiazem hydrochloride tablet dissolution profiles were compared using a statistical approach based on a mathematical model. A similarity region (SR) was defined based on the intra- and inter-lot parameter variances of the final production size standard lots. Statistical distances between the test and reference lot parameter means were computed and normalized. A 90% confidence region (CR) was developed around the statistical distance. The confidence region was compared with the similarity region to assess the similarity or dis-similarity of the test and reference (REF) lot dissolution profiles. Two test lots, one with a "minor' modification (mm) the other with a "major' modification (MM), were evaluated. RESULTS: "Weibull' was selected as the "model' function. A comparison of the confidence regions around the statistical distance of "mm-REF' and "MM-REF' with the similarity region, suggested that the dissolution profiles of the "minor' modification lot were similar and that of "major' modification lot were dis-similar to the reference lot. CONCLUSIONS: A "model dependent' approach was shown to be useful for the inter-lot in-vitro dissolution profiles comparison.

Cardiovascular Agents↗
PubMed2002

Unblocked statistical-coil tetrapeptides and pentapeptides in aqueous solution: a theoretical study.

NMR studies of the molecular conformations of peptides and proteins rely on a comparison of the relevant spectral parameters with the corresponding values for so-called statistical-coil polypeptides. For this reason, it is necessary to characterize the experimental ensemble of states populated by statistical-coil peptides. Such a characterization, however, has proven to be both difficult and sensitive to changes in many environmental parameters such as solvent composition, temperature, pH, as well as the neighboring amino acids in the sequence. As a consequence, a series of significant discrepancies has been reported for some experimentally observed parameters, such as chemical shifts, or vicinal coupling constants, (3)J(NHalpha), whose values appear to be incompatible with a statistical-coil ensemble. In this work, we report the results of a molecular mechanics study of a series of unblocked tetra- and pentapeptides under different pH conditions. These calculations were carried out with explicit consideration of both the coupling between the process of proton binding/release and conformation adopted by the molecule at a given pH and the contribution of the conformational entropy to the total free energy. Good agreement was found between the calculated and experimentally determined values of the vicinal coupling constant, (3)J(NHalpha), the alpha-proton chemical shift, and the (13)C(alpha) chemical shift. All the evidence accumulated in these theoretical calculations helps to rationalize some of the unsettled anomalies observed experimentally, and to provide an understanding of the effect of pH and amino acid sequence on the conformational preferences of statistical-coil peptides.

Amino Acids↗
PubMed2004

Statistical problems encountered in trapping studies of scolytids and associated insects.

Traps baited with semiochemicals are often used to investigate the chemical ecology of scolytids and associated insects. One statistical problem frequently encountered in these studies are treatments that catch no insects and, thus, have zero mean and variance, such as blank or control traps. A second problem is the use of multiple comparison procedures that do not control the experimentwise error rate. We conducted a literature survey to determine the frequency of these two statistical problems in Journal of Chemical Ecology for 1990-2002. Simulations were then used to examine the effects of these problems on the validity of multiple comparison procedures. Our results indicate that both statistical problems are common in the literature, and when combined can significantly inflate both the experimentwise and per comparison error rate for multiple comparison procedures. A possible solution to this problem is presented that involves confidence intervals for the treatment means. Options to increase the statistical power of trapping studies are also discussed.

Animals↗
PubMed1994

Misuse of statistical test in three decades of psychotherapy research.

This article reviews the misuse of statistical tests in psychotherapy research studies published in the Journal of Consulting and Clinical Psychology in the years 1967-1968, 1977-1978, and 1987-1988. It focuses on 3 major problems in statistical practice: inappropriate uses of null hypothesis tests and p values, neglect of effect size, and inflation of Type I error rate. The impressive frequency of these problems is documented, and changes in statistical practices over the past 3 decades are interpreted in light of trends in psychotherapy research. The article concludes with practical suggestions for rational application of statistical tests.

Humans↗
PubMed1997

Overcoming feelings of powerlessness in "aging" researchers: a primer on statistical power in analysis of variance designs.

A general rationale and specific procedures for examining the statistical power characteristics of psychology-of-aging empirical studies are provided. First, 4 basic ingredients of statistical hypothesis testing are reviewed. Then, 2 measures of effect size are introduced (standardized mean differences and the proportion of variation accounted for by the effect of interest), and methods are given for estimating these measures from already-completed studies. Power and sample size formulas, examples, and discussion are provided for common comparison-of-means designs, including independent samples I-factor and factorial analysis of variance (ANOVA) design, analysis of covariance designs, repeated measures (correlated samples) ANOVA designs, and split-plot (combined between- and within-subjects) ANOVA designs. Because of past conceptual differences, special attention is given to the power associated with statistical interactions, and cautions about applying the various procedures are indicated. Illustrative power estimations also are applied to a published study from the literature. It is argued that psychology-of-aging researchers will be both better informed consumers of what they read and more "empowered" with respect to what they research by understanding the important roles played by power and sample size in statistical hypothesis testing.

Aged↗
PubMed2003

When cues collide: use of stress and statistical cues to word boundaries by 7- to 9-month-old infants.

Prior research suggests that stress cues are particularly important for English-hearing infants' detection of word boundaries. It is unclear, though, how infants learn to attend to stress as a cue to word segmentation. This series of experiments was designed to explore infants' attention to conflicting cues at different ages. Experiment 1 replicated previous findings: When stress and statistical cues indicated different word boundaries, 9-month-old infants used syllable stress as a cue to segmentation while ignoring statistical cues. However, in Experiment 2, 7-month-old infants attended more to statistical cues than to stress cues. These results raise the possibility that infants use their statistical learning abilities to locate words in speech and use those words to discover the regular pattern of stress cues in English. Infants at different ages may deploy different segmentation strategies as a function of their current linguistic experience.

Attention↗
PubMed1983

Can statistics cause brain damage?

It is hoped that the comments made above will help contributors to the Journal of Cerebral Blood Flow and Metabolism identify weaknesses in their use of statistics. A little extra care in the presentation of results and adherence to the following guidelines should result in major improvement: (1) Give an explicit description of the type of statistical analysis used. (2) Increase the use of confidence intervals. (3) Use the Bonferroni correction (or other appropriate procedures) in multigroup comparisons. (4) Be aware of the assumptions underlying statistical methods and of weakness in experimental design. However, real benefits will be gained when statistics is viewed as being as important to the experiment as the choice of method for assessing cerebral blood flow itself.

Analysis of Variance↗
PubMed1991

The FDG/PET methodology for early detection of disease onset: a statistical model.

The development of appropriate statistical methodologies for neuroimaging studies is dependent upon the research question of interest. Often studies are analyzed with techniques that may not be appropriate for the research question but are accepted owing to convention, familiarity, or apparent statistical sophistication. Neuroimaging data are particularly complex owing to (a) the high number of potential dependent variables (i.e., regions of interest) coupled with the practical limitations on sample size; (b) the known physical properties of scanners (e.g., resolution) interacting with the intricate and variable structure of the human brain; and (c) mathematical properties introduced into the data by the physiological model for quantification. In this article, a statistical model will be discussed for addressing a particular problem in clinical studies. Given that there is a characteristic abnormality in regional glucose metabolism in a specific disease, can a probabilistic statement be made with confidence regarding the likelihood of an individual scan being similar to those from the disease group or normal subjects? The model capitalizes on known statistical aspects of normal regional glucose metabolism. To illustrate the model, data will be presented on normal subjects, patients with confirmed Huntington's disease, and subjects at risk for the disease. Reliability and clinical validity of the model will be discussed.

Adult↗
PubMed2006

Statistical pattern matching facilitates the design of polyvalent inhibitors of anthrax and cholera toxins.

Numerous biological processes involve the recognition of a specific pattern of binding sites on a target protein or surface. Although ligands displayed by disordered scaffolds form stochastic rather than specific patterns, theoretical models predict that recognition will occur between patterns that are characterized by similar or "matched" statistics. Endowing synthetic biomimetic structures with statistical pattern matching capabilities may improve the specificity of sensors and resolution of separation processes. We demonstrate that statistical pattern matching enhances the potency of polyvalent therapeutics. We functionalized liposomes with an inhibitory peptide at different densities and observed a transition in potency at an interpeptide separation that matches the distance between ligand-binding sites on the heptameric component of anthrax toxin. Pattern-matched polyvalent liposomes inhibited anthrax toxin in vitro at concentrations four orders of magnitude lower than the corresponding monovalent peptide, and neutralized this toxin in vivo. Statistical pattern matching also enhanced the potency of polyvalent inhibitors of cholera toxin. This facile strategy should be broadly applicable to the detection and neutralization of toxins and pathogens.

Animals↗
PubMed2004

Towards sound epistemological foundations of statistical methods for high-dimensional biology.

A sound epistemological foundation for biological inquiry comes, in part, from application of valid statistical procedures. This tenet is widely appreciated by scientists studying the new realm of high-dimensional biology, or 'omic' research, which involves multiplicity at unprecedented scales. Many papers aimed at the high-dimensional biology community describe the development or application of statistical techniques. The validity of many of these is questionable, and a shared understanding about the epistemological foundations of the statistical methods themselves seems to be lacking. Here we offer a framework in which the epistemological foundation of proposed statistical methods can be evaluated.

Genetic Techniques↗
PubMed1986

The trend toward increased use of statistics in published orthodontic articles.

There has been an almost twofold increase in the use of statistical procedures in the articles appearing in the American Journal of Orthodontics from 1975 to 1985. That increase is due primarily to the increase in articles using inferential statistics. This trend toward increased use and complexity of statistical procedures in published orthodontic articles suggests a need for orthodontists to be fully familiar with statistical procedures.

Journalism, Dental↗
PubMed2001

A practical method to statistically classify devices according to their relative accuracy.

Mathematical methods to statistically compare the relative accuracy of physiological monitoring devices to reference measurements are scarce. We developed such a method to compare any number of devices to each other as well as to reference values. This new statistical comparative procedure uses a combination of different known mathematical processes. The method allows the separation of the error of the devices into two components, the first, being systematic, can be easily amended, while the second, inherent to the technical limitations of the measuring device as well as to the physical properties of the explored phenomenon, cannot be corrected and will thus be used as the comparative criterion for statistics. That method, which is easy to implement should ease comparisons of the accuracy of any number of devices as well as comparison of other sets of physiological values, by giving an easy access to statistical results.

Equipment Design↗
PubMed2001

Accounting for overlap? An application of Mezzich's kappa statistic to test interrater reliability of interview data on parental accident and emergency attendance.

STUDY RATIONALE: The number of interview studies with service users is rising because of growth in health services research. The level of agreement between multiple interview data coders requires statistical calculation to support results. Basic kappa statistics are often used but this depends on having mutually exclusive data. Researchers should be aware that this is not valid when an interview word or paragraph can be coded into more than one category. The 'proportional overlap' kappa extension by Mezzich et al. (1981, Journal of Psychiatric Research 16, 29-39) has been investigated as an original solution. OBJECTIVES: To assess the level of agreement beyond chance between several raters of interview data by applying the 'proportional overlap' kappa statistic by Mezzich et al. to verbal interview data. The clinical area investigated was child attendance at an Accident and Emergency Department, where parental attendance experiences have been under-explored. METHODS: Two researchers using a coding schedule coded a random sample of interview transcripts. These data were applied to Mezzich's procedure; coder 1 notes that a paragraph refers to category A and B but coder 2 notes A, B and C. The total agreement overlap in this case was 0.66 because two actual agreements out of three possible agreements were made. This was repeated for each paragraph and divided by the number of coding pairs. All agreement values were summed then subsequently divided by the total number of paragraphs to get Po (total number of observed agreements) and by the total number of coding pairs to get Pe (total number of agreements by chance alone). Po and Pe were used in the basic kappa formula to assess interview coding reliability. RESULTS: The overall mean Po was 0.61, the mean Pe was 0.32, with a kappa score of 0.43; a moderate level of agreement which was statistically significant (t=4.8, P < 0.001, d.f.=23). CONCLUSION: Mezzich's procedure may be applied to interview data to calculate agreement levels between several coders.

Accidents↗