Shoptaw 2002.

Methods	Randomised 4‐arm controlled trial Country: USA Setting: 3 narcotic treatment centres in LA
Participants	175 smokers (≥ 10 CPD, expired CO > 8 ppm, cotinine > 30 ng/mL), av age 44, 39.5% women, av 22.1 CPD. No significant differences between groups, except group 3 reported higher cocaine use than other groups
Interventions	2‐week baseline and randomisation period, then 12 weeks treatment with NRT patches, tapered from 21 mg for 8 weeks, to 14 mg for 2 weeks and 7 mg for 2 weeks. CO and urine samples taken x 3/week. Randomised to: Group 1. NRT patch only Group 2 NRT patch + RP Group 3. NRT patch + CM: USD 2 for 1st CO sample < 8 ppm; each consecutive sample rewarded with voucher increased by USD 0.50, + bonus USD 5 for every 3 consecutive samples. If a sample > 8 ppm, reward process reverted to USD 2 level again, but was restored to previous scale after 1 round of 3 consecutive samples < 8 ppm. Participants could earn up to USD 447.50 Group 4. NRT patch + RP + CM (see group 3 procedure)
Outcomes	Baseline measures, + thrice‐weekly breath and urine samples throughout 12 weeks treatment, + weekly self‐report, and same measures at 6 months and 12 months. Participants with missing data were counted as continuing smokers
Notes	Additional outcome data supplied by the authors Study funded by National Institute on Drug Abuse, and National Cancer Institute
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "an urn randomization procedure". A randomised 2 x 2 repeated measures design
Allocation concealment (selection bias)	Unclear risk	Not stated
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Abstinence biochemically validated
Incomplete outcome data (attrition bias) All outcomes	Low risk	Group A (patch only): 6 months 5/43, 12 months 7/43 dropped out; Group B (patch + CM): 6 months 6/43, 12 months 8/43 dropped out