382,008 papers found

Meta-analyses pooling continuous outcomes can use mean differences (MD), standardized MD (MD in pooled standard deviation units, SMD), or ratio of arithmetic means (RoM). Recently, ratio of geometric means using ad hoc (RoGM (ad hoc) ) or Taylor series (RoGM (Taylor) ) methods for estimating variances have been…

OBJECTIVE: We aim to illustrate the potential impact of a new study on a meta-analysis, which gives an indication of the robustness of the meta-analysis. STUDY DESIGN AND SETTING: A number of augmentations are proposed to one of the most widely used of graphical displays, the funnel plot. Namely, 1) statistical signif…

BACKGROUND: Meta-analyses including a limited number of patients and events are prone to yield overestimated intervention effect estimates. While many assume bias is the cause of overestimation, theoretical considerations suggest that random error may be an equal or more frequent cause. The independent impact of random…

OBJECTIVE: Meta-analyses of continuous outcomes typically use mean differences (MDs) or standardized mean differences (SMDs) (MD in pooled standard deviation units). Ratio of means (RoM) is an alternative effect measure that performs comparably in simulation. We compared treatment effects and heterogeneity for RoM, MD,…

BACKGROUND: Many different microarray experiments are publicly available today. It is natural to ask whether different experiments for the same phenotypic conditions can be combined using meta-analysis, in order to increase the overall sample size. However, some genes are not measured in all experiments, hence they can…

BACKGROUND: There is growing interest in the study of gene-environment interactions in the context of genome-wide association studies (GWASs). These studies will likely require meta-analytic approaches to have sufficient power. METHODS: We describe an approach for meta-analysis of a joint test for genetic main effects…

BACKGROUND: Meta-analysis is a popular methodology in several fields of medical research, including genetic association studies. However, the methods used for meta-analysis of association studies that report haplotypes have not been studied in detail. In this work, methods for performing meta-analysis of haplotype asso…

Meta-analysis is the analysis of the results of multiple studies, which is typically performed in order to synthesize evidence from many possible sources in a formal probabilistic manner. In a simple sense, the outcome of each study becomes a single observation in the meta-analysis of all available studies. The methodo…

To evaluate the relative role of left and right hemispheres (RH) and describe the functional anatomy of RH during ortholinguistic tasks, we re-analyzed the 128 papers of a former left-hemisphere (LH) meta-analysis (Vigneau et al., 2006). Of these, 59 articles reported RH participation, providing 105 RH language contras…

No clear consensus has been reached at the methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism and Alzheimer's disease (AD) risk. Thus in this meta-analysis, a total of 19 case-control studies was assessed to evaluate the possible association. The data demonstrated that the frequency of T677 allele (T vs. C)…

The significance of risk effects in genetic association studies is assessed using the odds ratio for various genetic models (dominant, recessive and co-dominant) by merging genotypes. These models are not independent and there is no a priori biological justification for their choice. Consequently, the interpretation of…

Meta-analysis, a complex statistical method which involves synthesis of data from relevant studies to devise an effect size or a conclusion, has increasingly been recognized and impacts on evidence-based medicine, especially in the field of health science. Thanks to the advent and unmet need of evidence-based medicine,…

BACKGROUND: Weisberg et al. (Clin Trials 2009, 6: 109-18) illustrate that entry criteria in randomized trials can lead to results that are biased for the target population. Presenting data from a previously published meta-analysis of the effect of antidepressants in children on suicidality, they suggest a relationship…

Asymmetry in the funnel plot for a meta-analysis suggests the presence of dissemination bias. This may be caused by publication bias through the decisions of journal editors, by selective reporting of research results by authors or by a combination of both. Typically, study results that are statistically significant or…

OBJECTIVES: This article aims to (1) describe the steps in the development of a meta-analysis, (2) discuss the use of meta-analysis in developing an evidence base for case management practice, and (3) provide some basic guidelines for evaluating the meta-analysis. PRIMARY PRACTICE SETTINGS: Evidence-based practice (EB…

UNLABELLED: Several grafting materials have been used in sinus augmentation procedures including autogenous bone, demineralized freeze-dried bone (DFDBA), hydroxyapatite, beta-tricalcium phosphate (beta-TCP), anorganic deproteinized bovine bone and combination of these and others. Up to now a subject of controversy in…

MOTIVATION: Transcriptomic studies using microarray technology have become a standard tool in life sciences in the last decade. Nevertheless the cost of these experiments remains high and forces scientists to work with small sample sizes at the expense of statistical power. In many cases, little or no prior knowledge o…

OBJECTIVE: To illustrate the potential and challenges of the simultaneous analysis of a network of trials, using as a case study the investigation of the relative effectiveness of four topical fluoride treatments and two control interventions (placebo and no treatment) in preventing dental caries in children. STUDY DE…

MOTIVATION: The proliferation of public data repositories creates a need for meta-analysis methods to efficiently evaluate, integrate and validate related datasets produced by independent groups. A t-based approach has been proposed to integrate effect size from multiple studies by modeling both intra- and between-stud…

We study publication bias in meta-analysis by supposing there is a population (y, sigma) of studies which give treatment effect estimates y approximately N(theta, sigma(2)). A selection function describes the probability that each study is selected for review. The overall estimate of theta depends on the studies select…