Design
This randomized controlled cross‐over trial had two 14‐day intervention periods with an intervening 7‐day period of usual behaviour. Participants purchased their own cigarettes. They were instructed to smoke their usual brand from either one of two sizes of pack in each of two 14‐day intervention periods: (a) 25 cigarettes and (b) 20 cigarettes. Participants were randomized to the order in which they smoked from the two pack sizes (a–b; b–a).