title: We need to guard against bias.
authors.affiliation: School of Health and Social Care, Oxford Brookes University, Oxford, UK. david.foxcroft@brookes.ac.uk
authors.forename: David R
authors.initials: DR
authors.lastname: Foxcroft
authors.forename: Lesley
authors.initials: L
authors.lastname: Smith
mesh_terms: D006266:Health Education / Q000379:methods; D006801:Humans; D015201:Meta-Analysis as Topic; D010506:Periodicals as Topic; D017594:Publication Bias; D019966:Substance-Related Disorders / Q000517:prevention & control*