Abstract

This presentation reviews the use of Bayesian methods in meta-analysis of plant pathology studies. The use of meta-analysis has exploded over the last few years, as well as the use of Bayesian methods, facilitated by recent advances in computational technology. Whilst in most cases meta-analyses have been carried out using frequentist methods, there are a number of specific advantages conferred by the Bayesian approach. These include: full allowance for all parameter uncertainty in the models, the ability to include other ...

Note (first note only)

ARH 20 August 2012: DOI for other abstracts from same meeting: 10.1094/PHYTO.2009.99.6.S152

Abstract

BACKGROUND: It has been suggested that a time-lag bias exists whereby research studies with striking results are more likely to be stopped earlier than originally planned, published quicker, or both. If time-lag bias exists, new interventions might be mistakenly assumed to be effective. OBJECTIVES: To study the extent to which time to publication of a clinical trial is influenced by the significance of its result. SEARCH STRATEGY: Studies were identified by searching the Cochrane Methodology Register (The Cochrane Library, Issue 3, ...

Abstract

This dissertation is the culmination of a qualitative research study of evidence-based practicing occupational therapists. The purpose of this research was to examine perceptions of the learning conditions (i.e., personal, professional, and organizational) related to the occupational therapy practitioner's learning about evidence-based practice. Using a grounded-theory approach, this research study addressed the following research questions: (a) How does the occupational therapist practitioner perceive the learning conditions in regard to becoming an evidence-based practitioner? (b) Does the therapist experience the learning conditions ...

Abstract

Three methods: fixed intercept generalized model (GLM), random intercept generalized mixed model (GLMM), and conditional logistic regression (clogit) are compared in a meta-analysis of 43 studies assessing the effect of diet on cancer incidence in rats. We also perform simulation studies to assess distributional behavior of regression estimates and tests of fit. Other simulations assess the effects of model misspecification, and increasing the sample size, either by adding additional studies or by increasing the sizes of a fixed number of studies. ...

Abstract

Background: Systematic reviews (SRs) are increasingly viewed as useful decision-making tools yet the extent of SR publication bias is under-explored. Through my thesis, I aimed to investigate the extent of SR publication bias. Methods: A conceptual model was derived from literature searches and one-on-one interviews and three studies were conducted: a cross-sectional study of 296 SRs indexed in MEDLINE and published in November 2004, an international survey of 625 corresponding or first authors of a published SR in 2005, and a ...

Abstract

To better understand the influence of organizational and individual provider factors on evidence-based practice (EBP) implementation, the current study assessed attitudes toward EBP's, individual innovativeness, perceived organizational support for innovation, and EBP implementation among community mental health center (CMHC) clinicians ( N = 146). The objectives of the study were to: (1) examine the relationships between attitudes toward EBP's, individual innovativeness, and perceived organizational support for innovation and their association with EBP implementation; (2) test the indirect effects of organizational support ...

Abstract

This dissertation describes three methodological and content-based studies related to meta-analysis of HIV prevention research for men who have sex with men (MSM). First, we compared ANOVA models for individually- and group-randomized trials to derive the factors necessary to account for intraclass correlation (ICC) in three classic designs. For the simplest design, the factor is ( n -1) VIF / ( n-VIF ) where n is the number of participants per condition, and VIF is the variance inflation factor 1+( m ...

Abstract

This dissertation explores heterogeneity of treatment effects (HTE) and the role of subgroup analysis and the n-of-1 trial in determining evidence-based treatment for individuals. To explore HTE we conducted three studies. In the first study, we sampled randomized controlled trials to examine the appropriateness of methods used for subgroup analysis, and used logistic regression to determine predictors of correct analysis. Of 319 included RCTs we found that 92 reported HTE analysis using correct methods, while 88 used incorrect methods. Common covariates ...

Abstract

Prior work has identified evidence-based interventions (EBIs) based on whether interventions outperform control or alternative intervention conditions in randomized clinical trials. However, intervention effects can be assessed and examined in multiple ways. Consistently, different ways of gauging intervention effects yield inconsistent conclusions. Recently, a framework (Range of Possible Changes [RPC] Model) was developed to take into account inconsistent research findings in the identification of EBIs, by focusing on the instances in which interventions yield consistent effects. This investigation applies this framework ...

Abstract

Recent advances in microarray technology have enabled scientists to simultaneously gather data on thousands of genes. However, due to the complexity of genetic interactions, the functions of many genes remain unclear. The cause and progression of many diseases, like cancer and Alzheimer's, is increasingly being attributed to the deregulation of critical genetic pathways. Data mining is now being extensively used in biological datasets to infer gene function, and to identify genetic biomarkers for disease prognosis and treatment. There is a considerable ...

Abstract

Medical decisions should be based on good evidence. But this does not mean that health care professionals should practice evidence-based medicine. This dissertation explores how these two positions come apart, why they come apart, and what we should do about it. I begin by answering the descriptive question, what are current standards of evidence in medicine? I then provide a detailed critique of these standards. Finally, I address the more difficult normative question, how should we determine standards of evidence in ...

Abstract

Across fields, studies investigating the facilitators and barriers of EBP have been completed. There are a limited number of studies investigating facilitators and barriers regarding EBP within the Communication Sciences and Disorders (CSD) literature, and none to date investigating CSD student perceptions. The primary aim of this study was to examine and compare the perceptions of facilitators and barriers about EBP amongst graduate students in speech-language pathology and other allied health care training programs. The data collected raised various questions regarding ...

Abstract

Meta-analyses often consider the effect of a treatment on multiple, possibly related outcomes. Typically, summary estimates are derived from outcome-specific meta-analyses. Alternatively, a joint analysis can be conducted with a multivariate meta-analysis model, which also quantifies the correlation between the outcomes. This dissertation presents findings from analyses examining issues pertaining to the accuracy of the multivariate approach and its application to meta-analyses of longitudinal studies. Correlations measured in multivariate meta-analysis models can provide added insight about the treatment and disease. To ...

Abstract

The objective of this thesis is to acknowledge some of the different randomized trial designs and analytical approaches, as well as specific issues related to these. The thesis can be divided into two parts. The first part focuses on the validity of using randomization tests and tests based on meta-analysis techniques in the context of cluster randomized trials with binary outcomes. Reasons for making statistical inferences based on a randomization model rather than on a population model are discussed. Also, the ...

Abstract

Recent interest in interpretive reviews, which Grant and Graue nurtured during their editorship of the Review of Educational Research (1996-1999), points to new ways of thinking about the review of qualitative literature. Interpretivists seek approaches to reviewing that respect the spirit of interpretive inquiry and showcase the strengths of qualitative research. As methodologists have paid relatively little attention to the review of qualitative literature, reviewers have been left on their own to develop interpretive reviews. To contribute to the conversation on ...

Abstract

In the last few years, several studies have attempted to meta-analyze reliability estimates. The initial study, to outline a methodology for meta-analyzing reliability coefficients, was published by Vacha-Haase in 1998. Vacha-Haase used a very basic meta-analytic model to find a mean effect size (reliability) across studies. There are two main reasons for meta-analyzing reliability coefficients. First, recent research has shown that many studies fail to report the appropriate reliability for the measure and population of the actual study (Vacha-Haase, Ness, Nilsson ...

Abstract

Introduction. The impact of the inclusion/exclusion of grey literature in meta-analysis (MA) is unclear. Objectives. To investigate, in a sample of published MA; the prevalence of grey literature, the quality of reporting at the MA and trial levels, and the impact of grey literature on the point estimate and precision of the results. Methods. Analysis of Variance and regression models were used to consider the quality of reporting and the impact of grey literature on estimates of efficacy. Results. Grey literature ...

Abstract

Meta-analysis deals with the statistical synthesis of results from different studies. One important focus of meta-analysis has been the accurate estimation of the effect size, which is the difference between the means of the experimental and control groups, standardized by the (often assumed common) standard error. This dissertation applies the methods of robust statistics to effect size estimation. We first examine the problem of estimating the effect size from a single experiment. The generalization to two variables of the influence function ...

Abstract

In meta-analysis two practical problems are frequently encountered: dependent effect sizes from the same study or sample, and incomplete information in pooling correlation matrices. Common procedures for handling dependent effect sizes are to treat them as independent (effectwise procedure), or to average them within a sample (samplewise procedure). To handle missing data in pooling correlation matrices, the two common procedures are to include only studies providing all correlations of concern (listwise aggregation), or to include all studies that reported at least ...

Abstract

Meta-analysis is a statistical method which synthesizes results from a set of individual studies to estimate an overall effect. If the studies for a meta-analysis are chosen through a literature review, an inherent selection bias may arise, since for example, studies may tend to be published more readily if they are statistically significant, or deemed to be more ‘interesting’ in terms of the impact of their outcomes. This phenomenon, known as ‘publication bias’, may distort the results of a meta-analysis due ...

Abstract

The primary goal of the project was to explore differences in effect size estimates between Cohen's d and estimates using repeated measure and ANCOVA methods. Monte Carlo simulations using the GAUSS program (Aptech system, Inc., 1992) were used to compare Cohens d to the 14 effect size estimation methods of interest and to explore the variance of these methods. The computer simulations allowed investigation of whether the means and variances of the 14 effect size estimates matched the expected means and ...

Abstract

Meta-analysis is a set of statistical maneuvers to quantitatively summarize multiple related studies. There are two major statistical approaches to meta-analysis. One is fixed effect models, which assume that all studies are governed by a common treatment effect, and take the studies be analyzed as the universe of interest; the other is random effect models, which allow different treatment effects for different studies, and treat these studies as representing a sample from a larger population of possible studies. Because the reliability ...

Abstract

The result of a meta-analysis as part of a systematic review critically depends on the extent to which relevant information about the particular research question can be retrieved. Biases are especially to be expected due to the selective publication of significant results (publication bias). For the investigation of biases in meta-analyses, both (informal) graphical as well as statistical methods are used. Within the framework of a simulation study, two tests for biases are compared; a rank-correlation test (Begg and Mazumdar, 1994) ...

Abstract

The small sample studies typical of I/O psychology produce seemingly contradictory results, and reliance on statistical significance tests causes study results to appear even more conflicting. Meta-analysis is needed to integrate the findings across such studies to reveal the simpler patterns of relations that underlie research literatures, thus providing a basis for theory development. Meta-analysis can correct for the distorting effects of sampling error, measurement error, and other artifacts that produce the illusion of conflicting findings. This chapter discusses these artifacts ...

Abstract

The software META provides statistical methods for the performance of meta-analyses in medicine, psychology, and quality assurance in the pharmaceutical industry. META makes a variety of effect measures available, like the relative risk, the standardized difference, and quality indices. For these effect measures, classical pooled estimators as well as "modern" random effect models can be calculated, for example, the approach of DerSimonian and Laird (1986) or the mixture distribution approach (Böhning, 2000a; Böhning et al., 1998). The latter approach allows the ...

Abstract

Psychology researchers and practitioners are besieged by information. The traditional way of dealing with such information overload is to rely less on single primary studies, and more on literature reviews (including journal review articles and chapters in textbooks). These can help with the task of organizing and sifting the available evidence. Psychologists will be familiar with the traditional literature reviews, but a different sort of review, the systematic literature review can also be used as a method of scientifically testing hypotheses. ...

Abstract

This chapter examines the role of effect magnitude in psychological research. Measures of effect magnitude fall into one of three categories: (a) measures of effect size, (b) measures of strength association, and (c) other measures. The measures are used for three purposes: integrating the results of empirical research studies in meta-analyses, supplementing the information provided by null hypothesis significance tests, and determining whether research results are practically significant. (PsycINFO Database Record (c) 2007 APA, all rights reserved) ...

Abstract

Discusses the rhetorical structure of meta-analysis and demonstrates by exemplars the best way to utilize the information gathered with this technique to advance the building of theories about interpersonal communication. The author's major concern centered on how scholars could best structure their arguments about the magnitudes of the differences they uncover. (PsycINFO Database Record (c) 2007 APA, all rights reserved) ...

Abstract

(from the chapter) introduce literature search sources and methods that will be of use to the research synthesist / focus is on machine-readable databases relevant to the social, behavioral, and medical sciences service options [intermediary service providers, end-user search systems, CD-ROM search services] / database selection / structuring the search [the selection of representative terms, the use of controlled vocabulary, free-text searching, constructing the search strategy, hazards of constructing the search strategy] / citation searching / appendix: selected databases in the ...

Abstract

(from the chapter) discuss threats that apply to [the validity of] meta-analyses that seek only to describe the degree of association between two variables / discuss threats to the inferences that the nature of the relationship is causal in the "manipulability" or "activity" theory sense / [discuss] generalization, beginning with those validity threats that apply when generalizing to particular target populations, constructs, categories, and so on / examine the threats pertinent to analyses of potential moderator variables from which conclusions are ...

Abstract

(from the chapter) The purpose of this chapter is to review meta-analytic methods for synthesis of multivariate data in a social science context. The approach to multivariate meta-analysis presented here can be applied regardless of the form of the effect of interest (be it an effect size, correlation, proportion, or some other index). In general, the goals of a multivariate meta-analysis are the same as those of univariate syntheses: to estimate magnitudes of effect across studies, and to examine variation in ...