APA (7e ed.) Bronvermelding

Butterfiel, W. (1964). Effective personal letters (2nd rev.). Prentice Hall.

Chicago (17e ed.) Bronvermelding

Butterfiel, W. Effective Personal Letters. 2nd rev. Englewood Cliffs: Prentice Hall, 1964.

MLA (9e ed.) Bronvermelding

Butterfiel, W. Effective Personal Letters. 2nd rev. Prentice Hall, 1964.