EIPS‐Germany.

Methods	Allocation: randomised Blinding: not stated* Setting: Cologne, Bonn, Dusseldorf, Munich, Germany Inclusion criteria: ERIraos criteria, 18‐36 years Exclusion criteria: < 18 years and > 36 years, treatment with antipsychotics, history of psychotic episode, refusing enrolment in research studies, refusing psychopharmacological treatment, living out of area, moving out of area, delirium, dementia, amnesic or other cognitive disorder, mental retardation, psychiatric disorders due to somatic factor or related to psychotropic substances, alcohol or drug misuse in last 3 months, diseases of central nervous system (inflammatory, traumatic, epilepsy etc.)** Duration: 36 months (12 months' treatment + 24 months' follow‐up)
Participants	Diagnosis: risk for developing psychosis N = 128 Sex: men and women, ˜60:40% M:F Age: 18‐36 years, average ˜26, SD 6 years History: not reported
Interventions	1. IPI: individual CBT, group skills training, cognitive remediation and multifamily psychoeducation, up to 30 sessions. N = 63*** 2. Supportive counselling: support, psychoeducation and counselling, up to 30 sessions. N = 65***
Outcomes	Transition to psychosis: ERIraos, PANSS Leaving the study Functioning: GAF, SAS–II**** Mental state: PANSS (total, positive and negative score), MADRS
Notes	*Raters could have been aware of the treatment allocation. **Presence of inclusion criteria for the LIPS‐Germany was additional exit criteria from EIPS‐Germany study ***After randomisation, 2 in IPI group and 1 in supportive counselling group failed to attend any treatment sessions. ****15 participants not accounted for *****37 participants not accounted for Funding: German Federal Ministry of Education and Research Power analysis, sample size calculation: not reported Adherence: see Table 14
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Randomised by computer‐generated, by block, results placed in sealed envelopes and only opened at the time of treatment allocation
Allocation concealment (selection bias)	Unclear risk	Quote: "Using sealed envelopes." Comment: allocation concealment method insufficiently described; it is unclear whether envelopes were sequentially numbered and opaque.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Not reported in any of the manuscripts where this study was described. In the study protocol (NCT00204087) it was indicated: "Masking: None (open label)"
Blinding of outcome assessment (detection bias) All outcomes	High risk	Quote: "as well as in most trials involving psychosocial interventions it was extremely difficult to make assessments that are totally blind to the treatment condition. Although ratings were mainly carried out by people, who were not involved in treatment, raters could have been aware of the treatment allocation, which raises the possibility that rating bias could have influenced the results." Comment: high possibility that raters may not have been blinded.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Out of 128 randomised participants, 47 dropped out of the trial before its completion (attrition 37%). In the IPI group, attrition rate was 37% (N = 23, 1 withdrawn from intervention because of suspicion of organic brain disease and 22 lost to follow‐up: 3 moved, 19 did not return). In the supportive counselling group, attrition rate was 37% (N = 24, 24 lost to follow‐up: 7 moved, 17 did not return).
Selective reporting (reporting bias)	Low risk	All outcomes mentioned in registered protocol (NCT00204087) and publications' methods reported in the manuscript
Other bias	Low risk	We did not identify any other sources of bias.