Al‐Delaimy 2015

Methods	Design: Prospective cohort study Recruitment: Members of California Smokers Cohort (longitudinal survey), recruited proactively 2011 ‐ 2013 via telephone Setting: California, USA Inclusion criteria: state residents aged 18 ‐ 59 who had smoked at least 100 cigarettes during their lifetime and smoked cigarettes "at least some days" at baseline Exclusion criteria: Not stated
Participants	Total N: 1000 adult smokers (for this review, only include 236 ever EC users and 306 'will never use EC' respondents) 52.2% women; 30% 18 ‐ 44 years old, 70% 45 ‐ 59; 10% Hispanic, 73% non‐Hispanic white, 18% other; 83.6% daily smoker, 43% intended to quit smoking in next 6m
Interventions	Observational, no specific intervention. At baseline asked to indicate if they had used, might use, or would never use EC. Defined EC as “devices that look like cigarettes and contain nicotine but do not produce tobacco smoke; some brands are The Safe Cig, Green Smoke, and Blu.”
Outcomes	Self‐reported prolonged abstinence for 1m or longer, assessed via phone at 12m Also measured quit attempts, reduction
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	High risk	Observational study
Allocation concealment (selection bias)	High risk	Observational study
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Although there is no blinding, the study design and lack of intervention or contact with researchers mean that there is unlikely to be significantly impact on performance
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Telephone report, unblinded, but given nature of the study differential misreport seems unlikely
Incomplete outcome data (attrition bias) All outcomes	High risk	Greater loss to follow‐up for 'will never use’ than users
Selective reporting (reporting bias)	Unclear risk	Unable to determine prespecified outcomes