Cita APA (7th ed.)

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

Cita Chicago (17th ed.)

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

Cita MLA (9th ed.)

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