Dalton, Margaret Steig; Charnigo, Laurie (Setembro de 2004), «Historians and Their Information Sources»(PDF), College & Research Libraries: 400–25, at 416 n.3, cópia arquivada (PDF) em 10 de setembro de 2008, citing U.S. Dept. of Labor, Bureau of Labor Statistics (2003), Occupational Outlook Handbook; Lorenz, C. (2001), «History: Theories and Methods», in: Smelser, Neil J.; Bates, Paul B., International Encyclopedia of Social and Behavior Sciences, 10, Amsterdam: Elsevier, p. 6871.
Duff, Alistair (1996), «The literature search: a library-based model for information skills instruction», Library Review, 45 (4): 14–18, doi:10.1108/00242539610115263 ("A primary source is defined here as a source containing new information authored by the original researcher(s) and not previously published elsewhere.").
Dalton, Margaret Steig; Charnigo, Laurie (Setembro de 2004), «Historians and Their Information Sources»(PDF), College & Research Libraries: 400–25, at 416 n.3, cópia arquivada (PDF) em 10 de setembro de 2008, citing U.S. Dept. of Labor, Bureau of Labor Statistics (2003), Occupational Outlook Handbook; Lorenz, C. (2001), «History: Theories and Methods», in: Smelser, Neil J.; Bates, Paul B., International Encyclopedia of Social and Behavior Sciences, 10, Amsterdam: Elsevier, p. 6871.