Assessing consistency of responses to questions on cocaine use.

This study examines consistency of self-reported responses to items within the questionnaire of a multi-site, prospective study of drug abuse treatment in the United States (DATOS). The analyses use data from 2842 interviewer-administered intake interviews. Questions that were logically related are paired and responses compared. The questions cover three topics: (1) age at which different types of cocaine was used, (2) reports on most recent use and (3) frequency of cocaine use during period of "heaviest" use. Responses are coded as consistent, inconsistent, or as survey administration error. The latter is related to interviewer errors such as erroneous skip pattern, out-of-range responses, "don't know" responses, missing data, or illegible responses. Contrary to expectations inconsistent responses were relatively rare in this study, with fewer than 5% (0.5-4.6%) of respondents reporting inconsistent answers for pairs of logically related questions. A careful review of responses also found few survey administration errors (0.2-1.3%).