The primary data for analysis of behavioral responses to the experiment came from a series of face-to-face interviews administered three times a year, for the duration of the treatment period and at least one year beyond. These took about forty minutes each, were administered in the families' homes by specially trained interviewers, and were identical for both experimental and control group families.
Detailed questions on every aspect of labor force participation, earnings, and job change for the period since the previous interview were included in each questionnaire. The database thus contained a continuous work history on each family member (age 16 and over) from two years prior to enrollment until at least one year after treatment ended. In addition to the regular labor force core questions, each questionnaire included modules covering other aspects of behavior. In all, 53 questionnaire modules were developed, covering additional economic information such as consumption and wealth as well as family functioning, education, and social and psychological attitudes.
In addition to the rich body of information from these periodic interviews, Social Security and Internal Revenue Service records were collected so that validation studies of the interview-reported earnings information could be conducted.