Tuten 2012a.

Methods	RCT.
Participants	222 pregnant women provided written consent, but 143 were randomized. Pregnant women with an estimated gestational age of < 28 weeks who were opioid dependent and methadone stabilized. Average of 30.0 years old (SD = 5.2), 71.4% African American, 69.9% never married, 11.6 (SD = 1.5) mean years of education, 6.0% currently employed.   Exclusion: not receiving methadone maintenance, non‐compliant with study or CAP procedures, had a miscarriage or terminated the pregnancy, transferred programmes, or had a negative pregnancy test.
Interventions	Escalating reinforcement condition, earned a USD7.50 voucher for the first opioid negative and cocaine negative urine sample submitted. Voucher value increased by USD1/day on the specimen collection days until delivery or until the participant reached USD42.50 in earnings, after which earnings were capped and remained constant at this amount. If relapse occurred no reward for positive urine sample and value of voucher reset to USD7.50. Participants earned vouchers until delivery (n = 52). Fixed reinforcement condition, participants received a USD25 voucher each time they provided a drug‐negative urine sample. Participants who remained drug abstinent through the incentive period had total potential earnings of USD950. Earnings continued if it occurred after week 13. A drug positive sample or missed urine sample precluded voucher earnings, but earnings resumed upon submission of next drug free sample (n = 38). Attendance control condition, fixed and escalating participants were linked to an attendance control participant. Each time the fixed or escalating reinforcement participant received a voucher, the yoked participant received the same amount, regardless of urine test results for that individual. Control participants were not aware they were linked, but were told there was a chance that they might or might not be paid for delivering urine samples (n = 43). Study duration was 13 weeks or until delivery with 1 week of inpatient treatment (when participants could earn two vouchers and 12 outpatient weeks during which participants could earn three vouchers weekly).
Outcomes	Drug abstinence (number of urine screening tests negative for both opiates and cocaine, number of negative urine tests prior to the first positive test and longest consecutive number of negative urine tests), opioid use (with similar parameters as drug abstinence), cocaine use (with similar parameters).
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	"participants were randomly assigned to one of the treatment conditions within 5 days of program admission…" No specific description of randomization used.
Allocation concealment (selection bias)	Unclear risk	No mention of allocation concealment processes.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	"Ten cases were missing data on one or more of the concomitant variables so were dropped from the sample, reducing the final sample to 133 cases." Some information about attrition given, but breakdown of assignment groups and attrition was not provided.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	No mention of outcome assessor blinding.