Objective: The aim of our study is to compare the prevalence of illicit drug use estimated through a technique referred to as the "crosswise model" (CM) with the results from conventional direct questioning (DQ).
Method: About 1,500 students from Tehran University of Medical Sciences 2009-2010 were first interviewed by DQ and, then three months later, by the CM.
Result: The CM yielded significantly higher estimates than DQ for lifetime prevalence of use of any illicit drug (CM = 20.2%,DQ = 3.0%, p < .001) and for lifetime prevalence of use of opium or its residue (CM = 13.6%, DQ = 1.0%, p < .001). Also, for use of any illicit drug in the last month and use of opium or its residue in the last month, the CM yielded higher point estimates than DQ, although these differences were not significant (any drug: CM = 1.5%, DQ = 0.2%, p = .66; opium: CM = 3.8%, DQ = 0.0%, p = .21).
Conclusion: Our findings suggest that the CM is a fruitful data collection method for sensitive topics such as substance abuse.
Keywords: Iran; crosswise model; illicit drug use; randomized response technique; sensitive questions; substance abuse; survey methodology.