Recent reports indicate that radiation traces from this device have been discovered in sediment below the mountain.

Approaches[ edit ] In general, two types of evidence can be distinguished when performing a meta-analysis: The aggregate data can be direct or indirect.

AD is more commonly available e. This can be directly synthesized across conceptually similar studies using several approaches see below. On the other hand, indirect aggregate data measures the effect of two treatments that were each compared against a similar control group in a meta-analysis.

For example, if treatment A and treatment B were directly compared vs placebo in separate meta-analyses, we can use these two pooled results to get an estimate of the effects of A vs B in an indirect comparison as effect A vs Placebo minus effect B vs Placebo.

IPD evidence represents raw data as collected by the study centers. This distinction has raised the need for different meta-analytic methods when evidence synthesis is desired, and has led to the development of one-stage and two-stage methods.

Two-stage methods first compute summary statistics for AD from each study and then calculate overall statistics as a weighted average of the study statistics. By reducing IPD to AD, two-stage methods can also be applied when IPD is available; this makes them an appealing choice when performing a meta-analysis.

Although it is conventionally believed that one-stage and two-stage methods yield similar results, recent studies have shown that they may occasionally lead to different conclusions. Models incorporating study effects only[ edit ] Fixed effects model[ edit ] The fixed effect model provides a weighted average of a series of study estimates.

The inverse of the estimates' variance is commonly used as study weight, so that larger studies tend to contribute more than smaller studies to the weighted average. Consequently, when studies within a meta-analysis are dominated by a very large study, the findings from smaller studies are practically ignored.

This assumption is typically unrealistic as research is often prone to several sources of heterogeneity; e. Random effects model[ edit ] A common model used to synthesize heterogeneous research is the random effects model of meta-analysis.

This is simply the weighted average of the effect sizes of a group of studies. The weight that is applied in this process of weighted averaging with a random effects meta-analysis is achieved in two steps: Inverse variance weighting Step 2: Un-weighting of this inverse variance weighting by applying a random effects variance component REVC that is simply derived from the extent of variability of the effect sizes of the underlying studies.

This means that the greater this variability in effect sizes otherwise known as heterogeneitythe greater the un-weighting and this can reach a point when the random effects meta-analysis result becomes simply the un-weighted average effect size across the studies.

At the other extreme, when all effect sizes are similar or variability does not exceed sampling errorno REVC is applied and the random effects meta-analysis defaults to simply a fixed effect meta-analysis only inverse variance weighting.

The extent of this reversal is solely dependent on two factors: Indeed, it has been demonstrated that redistribution of weights is simply in one direction from larger to smaller studies as heterogeneity increases until eventually all studies have equal weight and no more redistribution is possible.

One interpretational fix that has been suggested is to create a prediction interval around the random effects estimate to portray the range of possible effects in practice. These advanced methods have also been implemented in a free and easy to use Microsoft Excel add-on, MetaEasy.

Thus it appears that in small meta-analyses, an incorrect zero between study variance estimate is obtained, leading to a false homogeneity assumption.

Overall, it appears that heterogeneity is being consistently underestimated in meta-analyses and sensitivity analyses in which high heterogeneity levels are assumed could be informative.

The authors state that a clear advantage of this model is that it resolves the two main problems of the random effects model. When heterogeneity becomes large, the individual study weights under the RE model become equal and thus the RE model returns an arithmetic mean rather than a weighted average.

This side-effect of the RE model does not occur with the IVhet model which thus differs from the RE model estimate in two perspectives: The latter study also reports that the IVhet model resolves the problems related to underestimation of the statistical error, poor coverage of the confidence interval and increased MSE seen with the random effects model and the authors conclude that researchers should henceforth abandon use of the random effects model in meta-analysis.

While their data is compelling, the ramifications in terms of the magnitude of spuriously positive results within the Cochrane database are huge and thus accepting this conclusion requires careful independent confirmation. The availability of a free software MetaXL [56] that runs the IVhet model and all other models for comparison facilitates this for the research community.

Models incorporating additional information[ edit ] Quality effects model[ edit ] Doi and Thalib originally introduced the quality effects model.

The strength of the quality effects meta-analysis is that it allows available methodological evidence to be used over subjective random effects, and thereby helps to close the damaging gap which has opened up between methodology and statistics in clinical research.

To do this a synthetic bias variance is computed based on quality information to adjust inverse variance weights and the quality adjusted weight of the ith study is introduced. In other words, if study i is of good quality and other studies are of poor quality, a proportion of their quality adjusted weights is mathematically redistributed to study i giving it more weight towards the overall effect size.

As studies become increasingly similar in terms of quality, re-distribution becomes progressively less and ceases when all studies are of equal quality in the case of equal quality, the quality effects model defaults to the IVhet model — see previous section.

A recent evaluation of the quality effects model with some updates demonstrates that despite the subjectivity of quality assessment, the performance MSE and true variance under simulation is superior to that achievable with the random effects model.

Network meta-analysis methods[ edit ] A network meta-analysis looks at indirect comparisons. In the image, A has been analyzed in relation to C and C has been analyzed in relation to b.

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However the relation between A and B is only known indirectly, and a network meta-analysis looks at such indirect evidence of differences between methods and interventions using statistical method. Indirect comparison meta-analysis methods also called network meta-analyses, in particular when multiple treatments are assessed simultaneously generally use two main methodologies.Critical Analysis of Research: Analyzing of Investigation should be clear and understandable for your readers as the purpose of the thesis statement is to present them what your critical analysis paper deals with.

that is the general information about making of critical analysis of articles, research papers and other research works that. The Medical Leadership, Education and Research Skills course is about supporting you in your role and enabling you to achieve your potential.

It will broaden your . History. The historical roots of meta-analysis can be traced back to 17th century studies of astronomy, while a paper published in by the statistician Karl Pearson in the British Medical Journal which collated data from several studies of typhoid inoculation is seen as the first time a meta-analytic approach was used to aggregate the outcomes of multiple clinical studies.

AN INTRODUCTION TO CRITICAL ANALYSIS OF PUBLICATIONS IN EXPERIMENTAL BIOMEDICAL SCIENCES THE RESEARCH PAPER IN BASIC MEDICAL SCIENCES Scientists publish research reports for a variety of reasons.

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