Higgins 2014 (AvB).

Methods	This 3‐armed randomised controlled trial aimed to investigate different schedules of financial incentives for smoking cessation in pregnant women and its impact on cessation. This study was conducted in Burlington VT in the USA between 2006‐2011 and women were recruited from obstetric practices and the Women, Infants, and Children (WIC) office.
Participants	Inclusion criteria: Smoking in the past 7 days, gestational age ≤ 25 weeks, residing within the county in which clinic is located, plan to remain in the geographical area for ≥ 6 months following delivery, and English speaking. Exclusion criteria:incarceration, previous participation in a voucher‐based incentive trial for smoking cessation, currently residing with a trial participant, regular use of opioid, psychomotor stimulant, or antipsychotic medications. Recruitment:43.8% participation rate (C = 42 I = 44). Baseline characteristics:Partner smokes % (A = 77 B = 85 C = 82) Mean age first started smoking (A = 15.2 B = 16.3 C = 14.9) Married% (A = 21 B = 18 C = 10). Progress + coding: Low SES, women were recruited from WIC.
Interventions	A: Control: In this condition, vouchers were delivered independent of smoking status. Voucher values were $15.00 per visit antepartum and $20.00 per visit postpartum, values that resulted in payment amounts comparable to average earnings in the CV condition in prior trials (Heil et al., 2008). All else was the same as in the CV and RCV conditions. B: Intervention 1: Usual contingent voucher condition (CV)—Vouchers redeemable for retail items were earned contingent on submitting breath CO specimens ≤ 6 ppm during the initial 5 days of the cessation effort. Beginning in Week 2, vouchers were delivered contingent on urine‐cotinine levels ≤ 80 ng/mL, a criterion that required a longer duration of smoking abstinence than breath CO (Higgins et al., 2007a). Voucher delivery was independent of self‐reported smoking status and based exclusively on meeting the biochemical‐verification criterion. Unauthorised failure to complete a scheduled assessment was treated as a positive test result consistent with an ITT approach (Friedman et al., 1998). Vouchers began at $6.25, and escalated by $1.25 per consecutive negative specimen to a maximum of $45.00, where they remained barring positive test results or missed abstinence monitoring visits. Positive test results or missed visits reset the voucher value back to the original low value, but 2 consecutive negative tests restored the value to the pre‐reset level. C: Intervention 2: Revised contingent voucher condition (RCV)—The same voucher schedule as outlined above was followed in this RCV condition except that potential earnings were rescheduled, moving $296.25 forward as bonuses available during Weeks 1–6 by meeting a ≤ 4 ppm breath CO criterion during Week 1, testing cotinine negative at the first urine test on the 2nd Monday of the quit attempt, and thereafter by submitting 2 cotinine‐negative specimens per week through Week 6. More specifically, bonuses earned by reaching a cut‐off of ≤ 4 ppm CO during Week 1 started at $18.75 and increased by $3.75 for each successive negative sample reaching a maximum potential bonus of $33.75 for the 5th consecutive negative specimen meeting the ≤ 4‐ppm CO cut‐off during Week 1. Women in this condition earned the same incentive as in the CV condition if they met the ≤ 6 ppm CO but not the ≤ 4 ppm cut‐off in Week 1. The goal was to provide bonuses for those who could achieve this more stringent criterion and thus decrease the likelihood of low‐level smoking that can undermine longer‐term abstinence (Higgins et al., 2006), but assure that a woman still received an incentive if she met the slightly more liberal criterion ≤ 6 ppm criterion effective in prior trials (Higgins et al., 2012). Testing cotinine‐negative on the 2nd Monday resulted in an additional bonus of $87.50 above usual CV incentive earnings on that date. 5 more bonuses of $15.50 each were available on Thursdays (2nd test day of each week) during Weeks 2–6 if a woman also had tested negative for smoking at the earlier test conducted that same week. Main Intervention Strategy: Incentives (multiple) v alternative intervention. Arms A and B are compared in this study ID, please see Higgins 2014 (AvC) for arms A and C. Intensity: Frequency (C = 6 I = 6) Duration (C = 6 I = 6).
Outcomes	Biochemically verified 7‐day smoking abstinence at 24 weeks' gestation*, Continued smoking at 12 weeks postpartum (0‐5 months)* Continued smoking at 24 weeks postpartum (6‐12 months)*, Birthweight*, LBW*, preterm births*, NICU admissions*, gestational age, estimated fetal growth (fetal weight gain, abdominal circumference, femur length, head circumference, biparietal diameter, lean thigh area.
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Women were randomised to the 3 different conditions, however does not explain how this was done.
Allocation concealment (selection bias)	Unclear risk	Not reported.
Incomplete outcome data (attrition bias) All outcomes	Low risk	All randomised women were included in the primary analysis with the exception of fetal demise (A = 3, B = 5, C = 4).
Selective reporting (reporting bias)	Low risk	Both primary and secondary outcomes reported.
Other bias	Low risk	No other bias detected.
Biochemical validation of smoking abstinence (detection bias)	Low risk	Smoking abstinence was biochemically validated, breath specimens were analysed using CO monitors and urine cotinine levels determined using onsite enzyme immunoassay testing
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Unclear.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported.
Incomplete implementation	Unclear risk	Unclear
Equal baseline characteristics in study arms	Unclear risk	Only 2 characteristics differed significantly between treatment conditions: more of those assigned to the RCV condition worked outside the home compared to the CV but not the NCV conditions, and those assigned to the RCV condition reported higher mean ratings of stress across past week than those assigned to the CV but not the NCV conditions (Table 1). These 2 characteristics were not significantly correlated with smoking abstinence or birth outcomes.
Contamination of control group	Low risk	As main intervention component was incentives, no risk of contamination of control group.