NLabs:10.1136/amiajnl-2012-001503 NLabs:10.1136/amiajnl-2013-002519 NLabs:10.1136/bjsm.2007.041822 NLabs:10.1136/tobaccocontrol-2011-050301 NLabs:10.1136/tobaccocontrol-2012-050831