Systematic review in the context of "Hierarchy of evidence"

Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in a defined population, and application of this knowledge to prevent diseases.

It is a cornerstone of public health, and shapes policy decisions and evidence-based practice by identifying risk factors for disease and targets for preventive healthcare. Epidemiologists help with study design, collection, and statistical analysis of data, amend interpretation and dissemination of results (including peer review and occasional systematic review). Epidemiology has helped develop methodology used in clinical research, public health studies, and, to a lesser extent, basic research in the biological sciences.

The Intergovernmental Panel on Climate Change (IPCC) is an intergovernmental body of the United Nations. Its job is to "provide governments at all levels with scientific information that they can use to develop climate policies". The World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) set up the IPCC in 1988. The United Nations endorsed the creation of the IPCC later that year. It has a secretariat in Geneva, Switzerland, hosted by the WMO. It has 195 member states who govern the IPCC. The member states elect a bureau of scientists to serve through an assessment cycle. A cycle is usually six to seven years. The bureau selects experts in their fields to prepare IPCC reports. There is a formal nomination process by governments and observer organizations to find these experts. The IPCC has three working groups and a task force, which carry out its scientific work.

The IPCC informs governments about the state of knowledge of climate change. It does this by examining all the relevant scientific literature on the subject. This includes the natural, economic and social impacts and risks. It also covers possible response options. The IPCC does not conduct its own original research. It aims to be objective and comprehensive. Thousands of scientists and other experts volunteer to review the publications. They compile key findings into "Assessment Reports" for policymakers and the general public; Experts have described this work as the biggest peer review process in the scientific community. The IPCC was the first of three global science policy panels to be established, followed by and IPBES (Intergovernmental Platform on Biodiversity and Ecosystem Services), established in 2012 and the Intergovernmental Science-Policy Panel on Chemicals, Waste and Pollution (ISPCWP) established in 2025.

Anecdotal evidence (or anecdata) is evidence based on descriptions and reports of individual, personal experiences, or observations, collected in a non-systematic manner.

The term anecdotal encompasses a variety of forms of evidence. This word refers to personal experiences, self-reported claims, or eyewitness accounts of others, including those from fictional sources, making it a broad category that can lead to confusion due to its varied interpretations. Anecdotal evidence can be true or false but is not usually subjected to the methodology of scholarly method, the scientific method, or the rules of legal, historical, academic, or intellectual rigor, meaning that there are little or no safeguards against fabrication or inaccuracy. However, the use of anecdotal reports in advertising or promotion of a product, service, or idea may be considered a testimonial, which is highly regulated in certain jurisdictions.

Meta-analysis is a method of synthesis of quantitative data from multiple independent studies addressing a common research question. An important part of this method involves computing a combined effect size across all of the studies. As such, this statistical approach involves extracting effect sizes and variance measures from various studies. By combining these effect sizes the statistical power is improved and can resolve uncertainties or discrepancies found in individual studies. Meta-analyses are integral in supporting research grant proposals, shaping treatment guidelines, and influencing health policies. They are also pivotal in summarizing existing research to guide future studies, thereby cementing their role as a fundamental methodology in metascience. Meta-analyses are often, but not always, important components of a systematic review.

The Cochrane Library (named after Archie Cochrane) is a collection of databases in medicine and other healthcare specialties provided by Cochrane and other organizations. At its core is the collection of Cochrane Reviews, a database of systematic reviews and meta-analyses that summarize and interpret the results of medical research. The Cochrane Library aims to make the results of well-conducted clinical trials readily available and is a key resource in evidence-based medicine.