“…Numerous studies have examined non-response bias in substance use surveys, but have shown no clear patterns of results. Compared to respondents in some research, non-respondents reported higher use of alcohol (Goldberg et al, 2006;Heath et al, 2001;McCoy et al, 2009;Torvik et al, 2012;Wild et al, 2001;Zhao et al, 2009), cigarettes (Boström et al, 1993;Cunradi et al, 2005;Goldberg et al, 2006;Hill et al, 1997;Korkeila et al, 2001;McCoy et al, 2009;Smith and Nutbeam, 1990;Torvik et al, 2012;Woodruff et al, 2000) or cannabis (Zhao et al, 2009). In contrast, some studies showed no significant differences between non-respondents and respondents on alcohol use (Cunradi et al, 2005;Gmel, 2000;Korkeila et al, 2001;Kypri et al, 2004;Strote et al, 2002;Trinkoff and Storr, 1997;Ullman and Newcomb, 1998), tobacco use (Strote et al, 2002;Ullman and Newcomb, 1998) or cannabis use (Ullman and Newcomb, 1998) outcomes.…”