Opium Use Reporting Error in Case-Control Studies: Neighborhood Controls vs. Hospital Visitor Controls

Abstract

Background There are relatively scant data to determine whether hospital visitors could serve as a proper source of controls in substance abuse case-control studies. The aim of this study was to evaluate using neighborhood versus hospital visitor controls in reporting opium use.Methods We conducted two independent case-control studies of cancer in Iran. In the first study, we selected controls from neighborhoods of the patients. For the second one, we selected controls among hospital visitors. In the latter study, hospital visitors could be companions of the patients or others visiting the hospital for any reasons except disease treatment from non-oncology wards of referral hospitals. Opium use and cigarette smoking information were self-reported in both studies.Results A total of 616 of neighborhood controls and 414 of hospital visitor controls were analyzed. Regular opium use among men was significantly higher in hospital visitors than neighborhood controls (43.3% vs. 32.2%, P=0.03) while the prevalence of regular cigarette smokers was very similar in both control groups (46.3 vs. 47.2, P=0.87). After adjusting for potential confounders using logistic regression, the differences of opium use between the two control groups became more pronounced (Adjusted OR=0.26, 95% CI: 0.10-0.69).Conclusions Because of the similarity of reporting cigarette smoking among neighborhood controls but substantially lower reporting of opium use among them, we concluded that neighborhood controls underreported opium use-a sensitive question- and that their use biases the findings in case-control studies. Hospital visitor controls may be more appropriate than neighborhood controls for studies of banned substances.