title: Sample bias may obscure results.
authors.forename: Euan M
authors.initials: EM
authors.lastname: Lawson
mesh_terms: D006801:Humans; D008385:Marijuana Smoking / Q000009:adverse effects*; D011605:Psychoses, Substance-Induced / Q000209:etiology*; D012107:Research Design; D015983:Selection Bias