A sample of 95 intravenous drug users agreed to provide urine samples, which would be tested for the presence of the metabolites of opiates and cocaine; the purpose of the study was to assess the validity of injection drug users' self- reported use of these drugs.

Using chi-square analyses, the researchers determined that there were no significant differences between intravenous drug users who agreed to participate in the study and those who declined to participate in terms of age, gender, ethnic group, education, primary drug of choice, treatment history, project intervention assignment, or time of follow-up. The urinalysis findings showed that 30 percent of the 67 participants who claimed to be drug-free over the previous 6 months had in fact used drugs. When compared to the total sample, the rate of misrepresentation fell to 21 percent. Logit regression analyses indicated that intravenous drug users who were black or whose primary drugs of choice were injected cocaine and crack were more likely than other groups to misrepresent their current drug use status. These findings demonstrate the need to corroborate self-report data with other, quantitative measures.