Showing papers on "Funnel plot published in 2008"

Contour-Enhanced Funnel Plots for Meta-Analysis:

Abstract: Funnel plots are commonly used to investigate publication and related biases in meta-analysis. Although asymmetry in the appearance of a funnel plot is often interpreted as being caused by publication bias, in reality the asymmetry could be due to other factors that cause systematic differences in the results of large and small studies, for example, confounding factors such as differential study quality. Funnel plots can be enhanced by adding contours of statistical significance to aid in interpreting the funnel plot. If studies appear to be missing in areas of low statistical significance, then it is possible that the asymmetry is due to publication bias. If studies appear to be missing in areas of high statistical significance, then publication bias is a less likely cause of the funnel asymmetry. It is proposed that this enhancement to funnel plots should be used routinely for meta-analyses where it is possible that results could be suppressed on the basis of their statistical significance.

More Than Numbers: The Power of Graphs in Meta-Analysis

Abstract: In meta-analysis, the assessment of graphs is widely used in an attempt to identify or rule out heterogeneity and publication bias. A variety of graphs are available for this purpose. To date, however, there has been no comparative evaluation of the performance of these graphs. With the objective of assessing the reproducibility and validity of graph ratings, the authors simulated 100 meta-analyses from 4 scenarios that covered situations with and without heterogeneity and publication bias. From each meta-analysis, the authors produced 11 types of graphs (box plot, weighted box plot, standardized residual histogram, normal quantile plot, forest plot, 3 kinds of funnel plots, trim-and-fill plot, Galbraith plot, and L'Abbe plot), and 3 reviewers assessed the resulting 1,100 plots. The intraclass correlation coefficients (ICCs) for reproducibility of the graph ratings ranged from poor (ICC = 0.34) to high (ICC = 0.91). Ratings of the forest plot and the standardized residual histogram were best associated with parameter heterogeneity. Association between graph ratings and publication bias (censorship of studies) was poor. Meta-analysts should be selective in the graphs they choose for the exploration of their data.

Publication bias as a threat to the validity of meta-analytic results

Abstract: This paper reviews the evidence in support of the contention that publication bias is a potential threat to the validity of meta-analytic results in criminology and similar fields. It then provides a critique of the traditional file drawer or failsafe N method for examining publication bias, and an overview of four newer methods that can be used to detect publication bias. These include two (trim and fill and cumulative meta-analysis) that enable the researcher to estimate the magnitude of the influence of publication bias on the overall mean effect size. Advantages and limitations of both traditional and newer methods are examined. The methods reviewed are illustrated through their application to a meta-analysis of the effects of drug courts on recidivism by Wilson et al. (Journal of Experimental Criminology, 2, 459–487, 2006).

Bench-to-bedside review: Avoiding pitfalls in critical care meta-analysis – funnel plots, risk estimates, types of heterogeneity, baseline risk and the ecologic fallacy

Abstract: Meta-analysis can be a powerful tool for demonstrating the applicability of a concept beyond the context of individual clinical trials and observational studies, including exploration of effects across different subgroups. Meta-analysis avoids Simpson's paradox, in which a consistent effect in constituent trials is reversed when results are simply pooled. Meta-analysis in critical care medicine is made more complicated, however, by the heterogeneous nature of critically ill patients and the contexts within which they are treated. Failure to properly adjust for this heterogeneity risks missing important subgroup effects in, for example, the interaction of treatment with varying levels of baseline risk. When subgroups are defined by characteristics that vary within constituent trials (such as age) rather than features constant within each trial (such as drug dose), there is the additional risk of incorrect conclusions due to the ecological fallacy. The present review explains these problems and the strategies by which they are overcome.

Cumulative funnel plots for the early detection of interoperator variation: retrospective database analysis of observed versus predicted results of percutaneous coronary intervention

Abstract: Objective To use funnel plots and cumulative funnel plots to compare in-hospital outcome data for operators undertaking percutaneous coronary interventions with predicted results derived from a validated risk score to allow for early detection of variation in performance. Design Analysis of prospectively collected data. Setting Tertiary centre NHS hospital in the north east of England. Participants Five cardiologists carrying out percutaneous coronary interventions between January 2003 and December 2006. Main outcome measures In-hospital major adverse cardiovascular and cerebrovascular events (in-hospital death, Q wave myocardial infarction, emergency coronary artery bypass graft surgery, and cerebrovascular accident) analysed against the logistic north west quality improvement programme predicted risk, for each operator. Results are displayed as funnel plots summarising overall performance for each operator and cumulative funnel plots for an individual operator’s performance on a case series basis. Results The funnel plots for 5198 patients undergoing percutaneous coronary interventions showed an average observed rate for major adverse cardiovascular and cerebrovascular events of 1.96% overall. This was below the predicted risk of 2.06% by the logistic north west quality improvement programme risk score. Rates of in-hospital major adverse cardiovascular and cerebrovascular events for all operators were within the 3σ upper control limit of 2.75% and 2σ upper warning limit of 2.49%. Conclusion The overall in-hospital major adverse cardiovascular and cerebrovascular events rates were under the predicted event rate. In-hospital rates after percutaneous coronary intervention procedure can be monitored successfully using funnel and cumulative funnel plots with 3σ control limits to display and publish each operator’s outcomes. The upper warning limit (2σ control limit) could be used for internal monitoring. The main advantage of these charts is their transparency, as they show observed and predicted events separately. By this approach individual operators can monitor their own performance, using the predicted risk for their patients but in a way that is compatible with benchmarking to colleagues, encapsulated by the funnel plot. This methodology is applicable regardless of variations in individual operator case volume and case mix.

Profound effect of study design factors on ventilator-associated pneumonia incidence of prevention studies: benchmarking the literature experience

Abstract: Background: The ventilator-associated pneumonia incident proportion (VAP-IP) is highly variable among control groups of studies of methods for its prevention. The objective here is to develop and validate a literature-derived benchmark against which these groups can be profiled. Methods: A literature search yielded 95 cohort groups and control and intervention groups of 150 studies of either non-antimicrobial or antimicrobial methods of VAP prevention. The 95 cohort groups comprise a benchmark set (30 groups), from which the reference funnel plot (RFP) was derived, and a search set (65 groups), against which the benchmark was validated. The VAP-IP data of the benchmark set were found in five published systematic reviews, whereas the VAP-IP data of the search set were

Study on stata software in investigating publication bias in meta-analysis

Abstract: [Objective]To explore the application of Stata software in investigating publication bias in meta-analysis[Methods]The corresponding commands of four methods in Stata9 software were applied to the analysis of the example in the study The four methods were funnel plot,Begg’s adjusted rank correlation test,Egger’s regression test,trim and fill method[Results]Fine plots,which were funnel plot,Begg’s funnel plot,Egger’s regression plot,trim and fill funnel plot,were produced by the four methods respectively The results of Begg’s test(z = 081,P = 0417)and Egger’s test(t = 119,P = 0254)were not statistically significant Four missing studies were filled by the trim and fill method LogRR and its 95%CI were 0022[-0015,0058]and 0012[-0021,0046]respectively before and after the application of trim and fill method[Conclusion]There is no publication bias in the meta-analysis of the example by the four methods The merit of Stata software is that it can complete to investigate publication bias in meta-analysis efficiently,quickly and conveniently

Meta-analyses with binary outcomes: how many studies need to be omitted to detect a publication bias?

Abstract: Meta- and pooled analyses are increasingly applied to aggregate the results of a number of studies, especially in health sciences. A typical difficulty is the presence of a publication bias. Usually Egger's regression test and funnel plots are applied to detect such a publication bias. A simulation study was conducted to investigate the quantity of null and negative results required to be omitted to detect a publication bias. In particular, the performance of Egger's test and funnel plots was considered in two scenarios with binary outcomes and expected odds ratios (OR) of 1 and 2, respectively. For both scenarios Egger's test detected only a small fraction of publication biases if few studies were deleted, corresponding to the results of a random deletion. Moreover, if a true null effect is present Egger's test is quite unlikely to detect a publication bias even if a considerable proportion of the null results are missing. Generally, the detection of a publication bias using Egger's test is only likely i...

The application of quantitative methods for identifying and exploring the presence of bias in systematic reviews: PDE-5 inhibitors for erectile dysfunction.

Abstract: A systematic review of PDE-5 inhibitors for erectile dysfunction was performed to evaluate the utility of quantitative methods for identifying and exploring the influence of bias and study quality on pooled outcomes from meta-analyses. We included 123 randomized controlled trials (RCTs). Methodological quality was poorly reported. All three drugs appeared highly effective. Indirect adjusted analyses showed no differences between the three drugs. Funnel plots and statistical tests showed no evidence of small-study effects for sildenafil whereas there was evidence of such bias for tadalafil and vardenafil. Adjustment for missing studies using trim and fill techniques did not alter the pooled estimates substantially. The exclusion of previous sildenafil nonresponders was associated with larger treatment effects for tadalafil. This investigation was hampered by poor reporting of methodological quality, a low number of studies, heterogeneity and large effect sizes. Despite such limitations, a comprehensive assessment of biases should be a routine in systematic reviews.

Oral cancer risk and smokeless tobacco products--clouded by smoke?

Abstract: Medline, Embase, Cancerlit, Toxline were searched, followed by the reference lists of identified reviews and articles. Human cohort or case–control studies in peer-reviewed journals or that were publicly available were selected if they specified study location; examined any form of oral cancer as the outcome; and described use of chewing tobacco, orally used moist snuff or unspecified smokeless tobacco as the exposure. Studies in Asian populations and those with insufficient power where risk estimates and confidence intervals were not reported or could not be calculated were excluded. Standard information was abstracted from each study. Whole-population data were used to estimate numbers of never-smokers. Separate figures for males and females were obtained where possible. Estimates were made of effect size and precision since these were not presented in original studies. Separate meta-analyses were conducted for chewing tobacco, for snuff and for overall smokeless tobacco. Sensitivity analyses for smokers/ nonsmokers were carried out. Heterogeneity was investigated and publication bias assessed using a funnel plot. The 32 studies meeting the inclusion criteria provided 38 heterogeneous study-specific estimates of odds or relative risk ratios (see Tables 1, 2). An increase in risk was mainly evident in studies conducted before 1980. No increase was seen in studies in Scandinavia. The pattern of estimates suggests some publication bias. Smokeless tobacco, as used in America or Europe, carries at most a minor increased risk of oral cancer, but elevated risks in specific populations or from specific products cannot definitely be excluded.

Meta-analysis of the relationship between product innovation and business performance

Abstract: Nowadays, conflicting research findings have been concluded on the relationship between product innovation and business performance To deep the understanding of the relationship between the two variables and resolve such inconsistent findings mentioned above, this paper uses meta-analysis which has received more and more attention in the field of management research to further analyze related studies quantitatively and comprehensively In the process of meta-analysis, this paper synthesizes samples as many as possible, and conducts a systematic review and deep analysis of extant literatures on product innovation and its influence on business performance Specially, the current research not only includes homogeneity test on extant studies, but also contains meta-analysis on the relationship between product innovation and business performance Besides, this paper uses funnel plot and Egger test to analyze publication bias Based on the results from meta-analysis, a positive and significant relationship between product innovation and business performance is found, which is followed by managerial implications, limitations, and future research directions