Participants were 238 "presidential scholars, historians and political scientists;" "Presidents 2010 Rank by Category," www.siena.edu, July 1, 2010
Participants were 65 "presidential historians" and "other professional observers of the presidency;" "C-SPAN 2009 Historians Presidential Leadership Survey," www.c-span.org, 2009
Participants were 8 correspondents, editors, bureau chiefs, columnists, and writers of The Times; "Who's the Greatest? The Times US Presidential Rankings," by Jeremy Griffin and Nico Hines, www.timesonline.co.uk, Oct. 28, 2008
Because of the short durations of their terms, William Henry Harrison and James Garfield were excluded from this ranking; participants were 85 "professors of history, law, political science and economics... the presidents are ranked in order of mean score, adjusted to give equal weight to Democratic- and Republican-leaning respondents;" "The Rankings," www.opinionjournal.com, Sep. 12, 2005
Participants were 32 "historians and close observers of presidential leadership;" "Rating the Presidents: Washington to Clinton," by Arthur M. Schlesinger, Jr., Political Science Quarterly, Summer 1997