RT Journal Article SR Electronic T1 Falling prevalence of smoking: how low can we go? JF Tobacco Control JO Tob Control FD BMJ Publishing Group Ltd SP 145 OP 147 DO 10.1136/tc.2007.021220 VO 16 IS 3 A1 Chapman, Simon YR 2007 UL http://tobaccocontrol.bmj.com/content/16/3/145.abstract AB