Meta-analysis is a review of studies (a study of studies) by combining results and studying conflicting results to better understand. Meta-analysis is the statistical procedure for combining data from multiple studies. it is used to identify effective treatments in medicine or trading systems and to plan new research.
In statistics, a meta-analysis refers to methods focused on contrasting and combining results from different studies, in the hope of identifying patterns among study results, sources of disagreement among those results, or other interesting relationships that may come to light in the context of multiple studies.
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.
As illustrated in the pyramid below, the quality of evidence increases from the lowest quality (expert opinion) studies and trails to systematic reviews: the highest level of evidence-based research.
source for the Quality of Evidence Pyramid: http://libguides.indstate.edu/ebp