Polowczyk 1993.

Methods	RCT Risk of Bias: Moderate Allocation concealment: Number of participants in control group: 305. Number of participants in intervention group: 225. This difference in the group size indicates that the randomisation procedure has not been satisfactory. Trial aim: To look for differences in data collected by consumers compared to data collected by health professionals in a patient satisfaction survey.
Participants	530 patients with serious and persistent mental illness who attended ten outpatient clinics were randomly assigned to be interviewed about their satisfaction with services by either a consumer or a professional. Setting: Ten outpatient clinics, three continuing treatment centres, and a psychosocial club, operated by the Kings Park Psychiatric Center, New York state. Country: USA.
Interventions	Type of process: Consumer involvement in research. The intervention group (225) was interviewed by consumers. The control group (305) was interviewed by professionals.
Outcomes	Interviewer effect measured by between‐group differences in level of patient satisfaction with mental health services.
Notes	Consumers were involved in research (patient satisfaction survey) as interviewers (data collectors).
Risk of bias
Bias	Authors' judgement	Support for judgement
Allocation concealment (selection bias)	Unclear risk	B ‐ Unclear