Killen 1999.

Study characteristics
Methods	Study design: parallel RCT Country: USA Recruitment: community volunteers responding to advertisements ‐ heavy smokers selected from responders
Participants	408 heavy smokers (> 25 cigarettes per day) 59% men; average age 47; average cigarettes per day: 36; modified FTND score: 18
Interventions	1) 25 mg nicotine patch for 6 weeks (16‐hour, no tapering) 2) 15 mg nicotine patch for 6 weeks Self‐help treatment manual, short video showing patch use and placement
Outcomes	Sustained abstinence at 12 months (7‐day PPA at both 6 and 12 months) Validation: saliva cotinine < 20 ng/mL (not required for 3 individuals not in area) Adverse events: measured at 24 hours, and 1, 2, 4 and 6 weeks (during treatment)
Notes	85% of self‐reported quitters provided samples for validation at 12 months This study was funded by the US Public Health Service Grant 1 R01 CA 68968 from the National Cancer Institute. Pharmacia and Upjohn AB (Sweden) provided the nicotine patches. Conflicts of interest: not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not stated
Allocation concealment (selection bias)	Unclear risk	Quote: "Smokers ... were randomized"
Blinding (performance bias and detection bias) All outcomes	Low risk	Quote: "Assignment to treatment dose was double‐blind"
Incomplete outcome data (attrition bias) All outcomes	Low risk	Participants leaving the area were excluded from analyses; all other unconfirmed claims of abstinence were counted as failures. Losses fully reported