Carroll 2006b.

Methods	RCT.
Participants	136 US marijuana‐dependent young adults referred by the criminal justice system.
Interventions	1. MET/contingency management (n= 33) 2. drug counselling/contingency management (n= 34) 3. MET (n= 35) 4. drug counselling (n= 33).
Outcomes	Physiological primary: Marijuana positive urine specimens (%). Non‐physiological primary: Days of marijuana use (%), longest duration of continuous abstinence, Secondary: None.
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	"...were randomised to one of the four treatment conditions"
Allocation concealment (selection bias)	Unclear risk	Insufficient information to permit judgment.
Blinding (performance bias and detection bias) Patients and providers	Low risk	No blinding, but most outcomes were physiological and also used to validate self‐reports, and not likely to be influenced by lack of blinding.
Blinding (performance bias and detection bias) Assessors	Low risk	Insufficient information to know whether assessors were blinded. But most outcomes were physiological and also used to validate self‐reports, and not likely to be influenced by lack of blinding.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	38% attrition at 3 months and 21% attrition at 6 months. Imbalance between groups. Reasons for missing data not stated. ITT was performed.
Selective reporting (reporting bias)	Low risk	The published report included all expected outcomes based on the stated hypotheses.
Other bias	Low risk	Urine toxicology screens and breath samples to check on self‐report. There were no differences between groups at baseline. No additional sources of bias appear to be present.