Killen 1997.

Methods	Setting: community, USA Recruitment: advertisements
Participants	424 smokers, 50% female, average age 42 to 47 years, average cpd 24
Interventions	2 × 2 factorial design. All participants received self‐help materials designed to help develop self‐control skills ∙ Self‐help and placebo patch ∙ Self‐help and nicotine patch (21 mg) ∙ As first bullet above and video, watched during initial office visit, and for use at home ∙ As second bullet above and video
Outcomes	Sustained abstinence (6 months and 12 months) Validation: saliva cotinine < 20 ng/mL
Notes	Test of additional materials With evidence of an interaction between nicotine and video conditions, nicotine arms entered separately via a dummy study
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Randomised in a 2 × 2 fully crossed factorial design; method not described
Allocation concealment (selection bias)	Unclear risk	No details given
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Unclear if participants not receiving video knew other participants were receiving it (and viewing it in a group); biochemical validation used
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Number lost to follow‐up not specified, but all participants included in denominators