Goldstein 1989.

Study characteristics
Methods	Study design: factorial RCT Country: USA Recruitment: community volunteers
Participants	89 smokers (excluding 18 early treatment dropouts not included in results)
Interventions	Factorial design of 2 types of group treatment, and 2 schedules for use of nicotine gum. Behaviour therapy arms combined. 1) Fixed‐schedule nicotine gum (2 mg); 1 piece/hour for 1st week with tapering over 10 weeks 2) Ad lib nicotine gum; to be used when urge to smoke, maximum 30/day
Outcomes	PPA at 6 months Validation: saliva cotinine < 10 ng/mL or CO < 8 ppm for people still using gum Adverse events: not measured
Notes	Each participant paid USD 130 at start of study, of which they recovered USD 30 for supplying follow‐up information. This study was funded by grant IN‐45Z from the American Cancer Society and by grant HL‐32318 from the National Heart, Lung, and Blood Institute. Conflicts of interest: not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Method not stated
Allocation concealment (selection bias)	Unclear risk	Quote: "each subject was assigned"
Blinding (performance bias and detection bias) All outcomes	High risk	Not relevant; placebo gum not used
Incomplete outcome data (attrition bias) All outcomes	Low risk	18 early dropouts (16.8%) not included. Dropout rate by EOT was 7.9%, by 6 months 3.4%; losses included as failures