title: Estimating the prevalence of illicit drug use among students using the crosswise model.
abstract: 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).
  
  
  METHODS
  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.
  
  
  RESULTS
  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).
  
  
  CONCLUSIONS
  Our findings suggest that the CM is a fruitful data collection method for sensitive topics such as substance abuse.
authors.affiliation: 1Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Mansour
authors.initials: M
authors.lastname: Shamsipour
authors.forename: Masoud
authors.initials: M
authors.lastname: Yunesian
authors.forename: Akbar
authors.initials: A
authors.lastname: Fotouhi
authors.forename: Ben
authors.initials: B
authors.lastname: Jann
authors.forename: Afarin
authors.initials: A
authors.lastname: Rahimi-Movaghar
authors.forename: Fariba
authors.initials: F
authors.lastname: Asghari
authors.forename: Ali Asghar
authors.initials: AA
authors.lastname: Akhlaghi
mesh_terms: D000428:Alcohol Drinking / Q000453:epidemiology; D055030:Drug Users / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D013287:Illicit Drugs; D007492:Iran / Q000453:epidemiology; D008297:Male; D015233:Models, Statistical; D015995:Prevalence; D012959:Socioeconomic Factors; D013334:Students / Q000706:statistics & numerical data*; D019966:Substance-Related Disorders / Q000453:epidemiology*; D011795:Surveys and Questionnaires
chemical_list: D013287:Illicit Drugs
keywords: Iran; crosswise model; illicit drug use; randomized response technique; sensitive questions; substance abuse; survey methodology