Elk 1998.

Methods	RCT.
Participants	12 cocaine‐dependent pregnant women: 58% African American, 8% Hispanic, 33% White; 92% never married or separated/widowed/divorced; 75% high school; 83% unemployed; 67% gravida 5 or more, 25% gravida 3 to 4; 75% in second trimester; DSM‐III‐R: 92% (10/11) cocaine primary drug of abuse, 8% (1/11) both heroin and cocaine dependent. Exclusion: Cessation of cocaine use greater than 30 days prior to enrolment.
Interventions	All received PNC, behaviourally‐based drug counselling, nutritional education, and HIV counselling. CM, $18 for each cocaine‐free urine sample, $20 weekly bonus if all 3 samples negative and perfect attendance (including PNC) (n = 6). Routine care. Duration unclear (at least 4 weeks) (n = 6).
Outcomes	Retention in treatment as number remaining in treatment. Abstinence as average of individual %. Attendance in PNC as number of visits. Perinatal outcomes as number of preterm labour, or preterm delivery, or both. ASI composite scores presented as a bar graph. All outcomes reported as chi square with P value only when significant.
Notes	Treatment facility provided free transportation and child care. We attempted to contact trial authors but received no response.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	"Following stratification on referral source (self vs. court or probation or parole), subjects were randomly assigned to one of two treatment groups…" No details provided related to randomization methods.
Allocation concealment (selection bias)	Unclear risk	Allocation concealment not described.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Attrition details outlined for the 12 women, all 12 carried throughout the analysis. Results have detailed participant numbers for each outcome.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	No references to outcome assessor blinding made.