Walker 2006.

Methods	Multisite RCT (4 sites).
Participants	97 US adolescents.
Interventions	2 session MET (n= 47) vs 3 months delayed condition (n= 50).
Outcomes	Physiological primary: None. Non‐physiological primary: Number of days of marijuana use. Secondary: None.
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	"...randomly assigned."
Allocation concealment (selection bias)	Unclear risk	Insufficient information to permit judgment.
Blinding (performance bias and detection bias) Patients and providers	High risk	No blinding.
Blinding (performance bias and detection bias) Assessors	Unclear risk	"Baseline and 3‐month follow‐up assessments were administered by an audio‐computer‐assisted self‐interviewing program." But "a different HE (health educator) was assigned to conduct the follow‐up."
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Attrition was 5% overall at 3 months follow‐up (9% in the MET group and 2% in the DFC group). Unbalanced across conditions. Reasons not reported. Stated use of ITT but reported only actual data.
Selective reporting (reporting bias)	High risk	Authors stated alcohol and other drugs as outcomes but reported only marijuana use in the results. Some results were only claimed as "not significant" but not reported explicitly.
Other bias	Unclear risk	Only self‐reported outcomes. There were more whites in the immediate treatment group than in the delayed treatment group at baseline.