Backstrom H. Charles. (1963). Survey research. Northwestern University Press.
Lua i Stíl Chicago (17ú heag.)Backstrom H. Charles. Survey Research. America: Northwestern University Press, 1963.
Lua MLA (9ú heag.)Backstrom H. Charles. Survey Research. Northwestern University Press, 1963.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.