“…To address the correlated effects problem I follow the current literature and control for school fixed-effects (McVicar and Polanski, 2014;Clark and Loheac, 2007;Lundborg, 2006;Ali and Dwyer, 2009;Fletcher, 2010;Pertold, 2009). School fixed-effects account for unobservable school-level characteristics that are common to all students in a school, such as school smoking policies, school resources spent on tobacco control programmes, and common background characteristics at the school-level.…”