ACKNOWLEDGEMENTS
We are grateful to Britt Kilian for her work on the data entry application used during data collection. We would also like to thank Wellcome for funding this work.British Columbia was excluded as cigarettes are only sold there in packs of 20 cigarettes. The Territories were excluded as the research agency did not have research panels there.One participant was allowed to shorten this to 6 days to avoid a clash with scheduled surgery.