APA-referens (7:e uppl.)

Sumner, W. G., & Keller, A. G. (1914). The challenge of facts, and other essays. Yale University Press.

Chicago-referens (17:e uppl.)

Sumner, William Graham, och Albert Galloway Keller. The Challenge of Facts, and Other Essays. New Haven: Yale University Press, 1914.

MLA-referens (9:e uppl.)

Sumner, William Graham, och Albert Galloway Keller. The Challenge of Facts, and Other Essays. Yale University Press, 1914.