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.
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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  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. 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. Multi-party period of Turkey Regional censorship predates the establishment of the Republic of Turkey. On 15 Februarythe Ottoman Empire issued law governing printing houses "Basmahane Nizamnamesi" ; books first had to be shown to the governor, who forwarded them to commission for education "Maarif Meclisi" and the police.
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If no objection was made, the Sultanate would then inspect them. Without censure from the Sultan books could not be legally issued.
The Press Law changed, sentences and fines were increased. It was given the power to confiscate publications, close papers and printing houses. Anyone not following the decisions of the commission were subject to imprisonment, between one and three years. During the s and s, broaching the topics of secularismminority rights in particular the Kurdish issueand the role of the military in politics risked reprisal.
For example, publisher Fatih Tas was prosecuted in under Article 8 at Istanbul State Security Court for translating and publishing writings by Noam Chomskysummarizing the history of human rights violations in southeast Turkey ; he was acquitted, however, in February Those who resist do so at their own risk.
Media censorship and disinformation during the Gezi Park protests NTV broadcast van covered with protest graffiti during the protests in Turkeyin response to relative lack of coverage of mainstream media of the protests, 1 June Foreign media noted that, particularly in the early days 31 May — 2 June of the Gezi Park proteststhe events attracted relatively little mainstream media coverage in Turkey, due to either government pressure on media groups' business interests or simply ideological sympathy by media outlets.
All of these have tended to steer clear of covering the demonstrations. Bianet recorded the censorship of websites, 40 Twitter accounts, news; attacks against 21 journalists, three media organs, and one printing house; civil pursuits against 28 journalists; and the six-fold increase of arrests of media representatives, with 24 journalists and 9 distributors imprisoned. The European Court of Human Rights condemned Turkey for violation of the freedom of expression in the Abdurrahman Dilipak case Sledgehammer investigation  and the Turkish Constitutional Court upheld the violation of the freedom of expression of five persons, including a journalist.
The Supreme Electoral Council ordered 65 channels twice to stop broadcasting the results of the June election before the end of the publishing ban. Attack to media freedom went far beyond the AKP interim government period. Mustafa Cambaz, a photojournalist working for the daily Yeni Safak was killed during the coup. Turkish soldiers attempting to overthrow the government took control of several newsrooms, including the Ankara-based headquarter of the state broadcaster TRT.
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They also forced a TV channel's anchor to read a statement at gunpoint while the member of the editorial board were held hostage and threatened. During the coup's night, in the streets of Istanbul, a photojournalist working for Hurriyet and the Associated Press was assaulted by civilians that were demonstrating against the coup.
Also, following the decision of declaring the state of emergency for three months taken on 21 July,  a series of limitation to freedom of expression and freedom of the media have been imposed. The measures within the regime of emergency include the possibility to ban printing, copying, publishing and distributing newspapers, magazines, books and leaflets.
In has never been an easy country for journalists, but I think today it has reached its lowest point and is experiencing unprecedented repression". Expressions of non-violent opinion are safeguarded by Article 10 of the European Convention on Human Rights and Fundamental Freedomsratified by Turkey inand various provisions of the International Covenant on Civil and Political Rightssigned by Turkey in Violating this norm can lead up to three years of detention.
As to the Internet, the relevant Law is Law No.