“…While a few studies among adolescents have found co-use to be associated with older age (Suris, Akre, Berchtold, Jeannin, & Michaud, 2007;Victoir, Eertmans, Van den Bergh, & Van den Broucke, 2007), a recent study of young adults found that co-users were younger than tobacco-only users (Ramo, Delucchi, Hall, Liu, & Prochaska, 2013). Some studies of adolescents and young adults have suggested a positive association between male sex and co-use (Guxens, Nebot, & Ariza, 2007;Penetar, Kouri, Gross, et al, 2005;Victoir et al, 2007), others have suggested a negative association (Ohene, Ireland, & Blum, 2005;Suris et al, 2007), and one found no correlation (Aung, Pickworth, & Moolchan, 2004). A number of studies have found African-American ethnicity (Aung et al, 2004;Vaughn, Wallace, Perron, Copeland, & Howard, 2008;White, Jarrett, Valencia, Loeber, & Wei, 2007) or multi-ethnicity to be associated with co-use (Ramo, Delucchi, Hall, Liu, & Prochaska, 2013).…”