Briefly, think tanks are organizations, institutions, or groups that conduct research, and produce and disseminate reports and policy recommendations. The focus of these organizations can range from as narrow as a single issue to very broad in interests. Politically they range from left to right, while some maintain a non-partisan position.
According to the Best Schools website, “one way to gauge the influence of a think tank is to focus on the scholars active in it, their record of publications and other scholarly achievements, and how deeply these have affected the culture’s climate of opinion." (http://www.thebestschools.org/features/most-influential-think-tanks/)
The widely recognized rankings from the University of Pennsylvania Think Tanks and Civil Societies Program bases its rankings on an organization's ability to retain top-level analysts, the rigor of its research, its access to policy makers, and its influence on policy.
In an opinion piece on Think Tanks: Independent Research, Ideas, and Advice. presents another view. This Library guide expresses an opinion simply by which think tanks are included and which ones are omitted.
Generally, those included have been noted in journal article and reviews or web rankings. They are present here in alphabetical order. For more detail and a search tool, follow the Penn link, above.
Ella Strattis, Research & Instructional Services. Email: firstname.lastname@example.org. Tel: 856-256-4975