A new report by Transparify shows that the conservative think tanks American Enterprise Institute (AEI), Hudson Institution, and Hoover Institute all got the ultra-low rating of one-star for being "highly opaque" in terms of their funding sources.
However, the Heritage Foundation, the US's most well-known conservative think tank, received the much higher rating of "broadly transparent," (four stars) along with its center-left cohort the Brookings Institution. Other think tanks that are "broadly transparent" include Atlantic Council, Carnegie Endowment for International Peace, Center for a New American Security (CNAS), Center for Strategic and International Studies (CSIS), and Center for American Progress (CAP).
The Wilson Center, Stimson Center, and Center for Global Development (CGD) are among the major US think tanks that received the highest ranking of five stars ("highly transparent").
Transparify rates the extent to which think tanks publicly disclose through their website where their funding comes from. The average transparency score among US think tanks is 3.3 stars, up from just 2.1 stars in 2013. The Transparify survey rated 200 think tanks in 47 countries.
Transparify is funded by the Think Tank Fund, a program of the Open Society Foundations which is funded by billionaire George Soros. Ironically, in the Transparify report, Open Society Foundations got the worst score of any "think tank," with zero stars.
The full report can be found here.
Update: After the data for the Transparify report was collected, the Hudson Institute became a 4-star think tank due to its funding disclosures in its 2015 annual report. Among the $100,000+ donors to Hudson include: 21st Century Fox, Dow Jones, John D. and Catherine T. MacArthur Foundation, PhRMA, Sarah Scaife Foundation, and the Taipei Economic and Cultural Representative Office in the US. Other donors to Hudson include AT&T, BHP Billiton, State Farm, United Parcel Service (UPS), Wendy's Corporation, Chevron, and Exxon Mobil.
Here is an article in iNews by Cahal Milmo about the new Transparify report entitled "Leading Think Tanks 'Influencing Public Policy Without Disclosing Donors.'"