Sells 2008.

Methods	Allocation: randomised Blindness: not stated Study duration: 12 months Location: single centre Design: parallel Setting: not stated Country: USA Consent: written
Participants	Diagnosis: psychotic disorder, major mood disorder, substance use disorder, co‐occurring disorders N = 137 History: not stated Sex: men 84, women 53 Age: mean 41, SD 9 years Length of illness: not stated Exclusion criteria: not stated
Interventions	Group 1: peer‐based intensive case management group (n = 68). Content: peers used past experiences with recovery as a tool for understanding, role modelling and hope building for others. Participants received 1 year of service from intensive case management teams that included peer providers as primary contacts. Delivered by: peer providers who had severe mental illness history. Frequency: not stated. Treatment duration: 12 months. Group 2: traditional intensive case management group (n = 69). Content: traditional intensive case management. Treatment duration: 12 months.
Outcomes	Peer outcomes: impact on participant and peer supporter Unable to use Leaving the study early (only missing data in scale) Behaviour: drug and alcohol use (no data were reported) Peer outcomes: favourable therapeutic relationship change (no SD data were reported), quality of life for participant and peer supporter (no data reported)
Notes	Funding source: Yale Institution for Social and Policy Studies; the peer‐based treatment option was sponsored by the Connecticut Department of Mental Health and Addiction Services.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "investigators randomly assigned participants to either the experimental (peer provider) or control (regular treatment) condition." Comment: insufficient information to make judgement.
Allocation concealment (selection bias)	Unclear risk	Comment: author did not describe allocation concealment. Insufficient information to make judgement.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Comment: author did not describe blinding of participants and personnel. Insufficient information to make judgement.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Comment: author did not describe blinding of outcome assessment. Insufficient information to make judgement.
Incomplete outcome data (attrition bias) All outcomes	High risk	Comment: 26 participants left early from the intervention group and 38 participants left early from the control group (data extracted from Table 2); total attrition rate in control group was higher than 50%. Reasons for missing outcome data not reported.
Selective reporting (reporting bias)	High risk	Comment: study protocol not available. Author did not report adequate data for favourable therapeutic relationship change, quality of life, and drug and alcohol use.
Other bias	Low risk	Not noted.