A man’s report of his own behavior is widely used in the social sciences, from cultural anthropology to psychophysics, and the reliability of the informant or subject is a crucial issue. So is the nature of the data obtained. What are the actual facts in these sciences? A survey of opinions or attitudes, with a questionnaire or interview, may tell us what a man says he tends to do, but is the tendency or the statement of the tendency the actual datum? (p. 139)
