Mahlke 2017.

Methods	Allocation: randomised Blindness: not stated Study duration: 12 months Location: multicentre Design: parallel Setting: inpatients and outpatients Country: Germany Consent: written
Participants	Diagnosis: severe mental illness (28% schizophrenia and schizoaffective disorders, other diagnose including bipolar disorder, unipolar depression, or personality disorder) N = 216 History: > 2 years Sex: men 92, women 124 Age: mean 41.48, SD 12.28 years Exclusion criteria: primary diagnosis of drug or alcohol abuse and insufficient command of German to communicate with the peer supporters.
Interventions	Group 1: peer‐support group + standard care (n = 114). Content: 1‐to‐1 peer support in addition to treatment as usual. Peer supporters contacted patients within the first week after randomisation and then established 1‐to‐1 meetings. The minimum number of meetings required to build a supporting relationship and be effective for the patient, based on the experiences in delivering support by the peers themselves. Delivered by: peers and staff, who trained by a peer worker and a psychologist. Frequency: 4 and 26 times for 1 hour over a 6‐month period. Treatment duration: 6 months. Group 2: standard care (n = 102). Content: inpatient and outpatient care with infrequent meetings with outpatient psychiatrists, and access to community‐based groups and separate psychological treatments. Treatment duration: 6 months.
Outcomes	Service use: duration of hospital stay Global state: severity of illness (Clinical Global Impression scale) Behaviour: self‐efficacy Leaving the study early Functioning: general Peer outcomes: quality of life for participant and peer supporter
Notes	Funding sources: part of the 'psychenet' project (www.psychenet.de) and received funding from the Federal Ministry of Education and Research in Germany from 2011 to 2015 (BMBFNr: O1KQ1002B).
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "The participants were randomly allocated to either one‐to‐one peer support or the control group in a 1:1 ratio, stratified by hospital, in blocks of 20." Comments: adequate sequence generation.
Allocation concealment (selection bias)	Low risk	Quote: "An independent statistician, ... produced randomly generated treatment allocations ... within sealed, numbered, opaque envelopes that were stored and inaccessible to the trial team." Comments: allocation concealment ensured.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Comment: the author did not describe the blinding of participants and personnel. Insufficient information to permit judgement of low risk or high risk.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Comment: the author did not describe the blinding of outcome assessment. Insufficient information to permit judgement of low risk or high risk.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Quote: "Whilst the dropout rate on the primary outcome was 31%, it was substantially higher on the clinician‐rated secondary outcomes." Comments: moderate attrition rate.
Selective reporting (reporting bias)	High risk	Comment: study protocol registered on ClinicalTrials.gov (NCT02276469). Illness of management and satisfaction of the client was not reported.
Other bias	Low risk	None noted.