TABLE 1.

Ratio of estimates of prevalence of drug use obtained in self-administered versus interviewer-administered questionnaires.

	Lifetime	Last 12 months	Last 30 days
Alcohol	0.99	1.04	1.06
Marijuana	1.05	1.30	1.61
Cocaine	1.06	1.58	2.40

Note. Ratios are weighted proportions of respondents reporting use of drug in self-administered questionnaire (SAQ) divided by proportion of respondents reporting use of drug in interviewer-administered questionnaire (IAQ) format. Estimates of proportions are derived from survey of 3,326 respondents who were randomly assigned to either IAQ or SAQ conditions. Respondents were a probability sample of persons 12 years of age and older residing in 33 purposely-sampled metropolitan areas in the U.S.A. in 1990.

Source: Turner et al. (1992:187, Fig. 7-1).