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Analysis dissertation

Analysis dissertation to navigation Jump to search For the process in historical linguistics known as metanalysis, see Rebracketing.

Graphical summary of a meta analysis of over 1,000 cases of diffuse intrinsic pontine glioma and other pediatric gliomas, in which information about the mutations involved as well as generic outcomes were distilled from the underlying primary literature. A meta-analysis is a statistical analysis that combines the results of multiple scientific studies. The basic tenet behind meta-analyses is that there is a common truth behind all conceptually similar scientific studies, but which has been measured with a certain error within individual studies. The aim then is to use approaches from statistics to derive a pooled estimate closest to the unknown common truth based on how this error is perceived.

A key benefit of this approach is the aggregation of information leading to a higher statistical power and more robust point estimate than is possible from the measure derived from any individual study. Meta-analyses are often, but not always, important components of a systematic review procedure. For instance, a meta-analysis may be conducted on several clinical trials of a medical treatment, in an effort to obtain a better understanding of how well the treatment works. The term «meta-analysis» was coined in 1976 by the statistician Gene V. Glass, who stated «my major interest currently is in what we have come to call the meta-analysis of research. A meta-analysis is a statistical overview of the results from one or more systematic reviews. The precision and accuracy of estimates can be improved as more data is used.

Inconsistency of results across studies can be quantified and analyzed. A meta-analysis of several small studies does not predict the results of a single large study. Some have argued that a weakness of the method is that sources of bias are not controlled by the method: a good meta-analysis cannot correct for poor design or analysis in the original studies. Dissertation funnel plot expected without the file drawer problem.

Abstract in a dissertation

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A funnel plot expected with the file drawer problem. Another potential pitfall is the reliance on the available body of published studies, which may create exaggerated outcomes due to publication bias, as studies which show negative results or insignificant results are less likely to be published. Apart from the visual funnel plot, statistical methods for detecting publication bias have also been proposed. These are controversial because they typically have low power for detection of bias, but also may make false positives under some circumstances. A Tandem Method for analyzing publication bias has been suggested for cutting down false positive error problems. This Tandem method consists of three stages.

Firstly, one calculates Orwin’s fail-safe N, to check how many studies should be added in order to reduce the test statistic to a trivial size. However, low power of existing tests and problems with the visual appearance of the funnel plot remain an issue, and estimates of publication bias may remain lower than what truly exists. Most discussions of publication bias focus on journal practices favoring publication of statistically significant findings. However, questionable research practices, such as reworking statistical models until significance is achieved, may also favor statistically significant findings in support of researchers’ hypotheses.

Studies often do not report the effects when they do not reach statistical significance. Maximum likelihood estimation of the meta-analytic effect and the heterogeneity between studies. Multiple imputation of the NSUEs adding noise to the estimate of the effect. Separate meta-analyses for each imputed dataset. Pooling of the results of these meta-analyses.

A 2011 study done to disclose possible conflicts of interests in underlying research studies used for medical meta-analyses reviewed 29 meta-analyses and found that conflicts of interests in the studies underlying the meta-analyses were rarely disclosed. First, there is evidence in the record supporting the accusation that EPA «cherry picked» its data. Without criteria for pooling studies into a meta-analysis, the court cannot determine whether the exclusion of studies likely to disprove EPA’s a priori hypothesis was coincidence or intentional. 6 of and the Appendices to EPA’s «Respiratory Health Effects of Passive Smoking: Lung Cancer and other Disorders».

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As a foreigner, I know very little about Australian politics.

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