Self-Correction of Unreported Marijuana Use by Participants Taking a Street Intercept Survey

Background: Due to underreporting, a major challenge associated with drug use surveys is obtaining precise estimates of drug use. Objective: This study examined reliability of self-reported lifetime marijuana use among electronic dance music (EDM) party attendees - a high-risk population for drug use. Methods: 794 adults (35.1% female) entering EDM parties were intercept-surveyed. Participants were asked about lifetime marijuana use early in the survey. Those not reporting use were asked 5-10 min later if their earlier response was correct. Participants reporting their original response was not correct were asked to check off a reason why they did not originally report use. Participants were also asked at the end of the survey how honestly they responded throughout the survey. Prevalence of lifetime marijuana use with and without corrected responses was compared and risk factors for underreporting were examined using a Poisson generalized linear model. Results: Among those not reporting marijuana use, 31.2% subsequently reported use when asked again. Prevalence of use increased from 73.7% to 81.9% after correcting responses, an 8.2% absolute increase and a 10.0% relative increase. Reporting lifetime use of ecstasy and/or LSD was associated with lower risk for underreporting marijuana use. Compared to those reporting that they answered all questions honestly, those who reportedly answered most or no questions honestly were at higher risk for underreporting. Conclusion: Asking participants to confirm previous responses can help detect underreporting of drug use on intercept surveys. Results can inform survey methods when participants are believed to be at risk for underreporting.