The combination of two surveys conducted in 2005 provided a sample of approximately 33,000 individuals aged 18 to 64, enabling an examination of how the data collection method influences the measurement of the prevalence of sensitive behaviors such as psychoactive substance use: the Life Events and Health (EVS) survey was conducted using a self-administered computer-based questionnaire with audio prompts (Audio-CASI), whereas for the 2005 Health Barometer survey, data collection was conducted using Computer-Assisted Telephone Interviewing (CATI). This document is a chapter from the following book: Tremblay ME, Lavallée P, El Haj Tirari M. Survey Practices and Methods. Paris: Dunod; 2011. 382 p.