Crowley 1995.

Methods	Country: USA Setting: outpatient smokers at a Denver COPD clinic Design: 3‐arm randomized controlled trial
Participants	49 smokers (18 experimental group, 16 cigarette self‐report group, 15 control group), age at least 35 with COPD, breath CO > 14 ppm and FEV < 70% of FVC. Exclusion criteria: absence from study region, job exposure to high CO, pregnancy, other serious health or dental conditions, elevated bilirubin or blood urea nitrogen. 12 (24%) female, average age 61.4, average FEV 49.5% of normal value. No baseline imbalances.
Interventions	All participants had daily CO monitoring performed by a study technician over 85 days, + brochure + nicotine gum. At start of study participants were given 3 Colorado Lottery tickets to quote: “throw cigarettes down the toilet”. All were given 1 lottery ticket per day for quote: “time and effort”. Experimental group: received lottery ticket reward for every CO test < 10 ppm. Cigarette self‐report group: received lottery ticket reward for each self‐reported abstinence since previous visit. Control group: each pt received (irrespective of their own abstinence) the same reward as an experimental participant with whom they had been paired. Measurement intervals and payment schedules were changed frequently.
Outcomes	Verified 24‐hour PPA, measured at 6 months (CO corrected for air pollution < 10 ppm, also verified using urinary cotinine and blood oxygen saturation). Corrected CO relative to number of cigarettes reported.
Notes	Also in ISC.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not stated.
Allocation concealment (selection bias)	High risk	Participants stratified by sex and FEV and groups allocated randomly, such that within each stratum, a participant was always assigned to the experimental group before a participant could be assigned to the control group.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Biochemical validation used in addition to self‐report.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Dropout: experimental group 4/18; cigarette self‐report group 4/16; control group 1/15. 4/40 moved away or died. An ITT analysis was conducted.
Other bias	High risk	Paper does not report 6‐month cessation outcome per group, but only figures for all groups combined after noting non‐significant differences.