OPUS II.

Study characteristics
Methods	Study design: individually‐RCT Duration: 36 months extension of SEI. Two‐year duration standard SEI (prior to trial) is followed by three‐year extension of ESEI (in intervention arm). Total SEI plus ESEI duration was five years Setting: community‐based mental health team, Denmark Recruitment method: all patients receiving treatment for first‐episode psychosis in OPUS teams recruited an average of 19 months into their 24 months standard treatment
Participants	Diagnosis: majority schizophrenia diagnosis (74.6% versus 74.9% in the extended SEI, and standard SEI + TAU arms, respectively) Sample size: 400 participants randomised Age: mean age of 25.6 (SD 4.3) Sex: 53.7% male and 43.3% male in the extended SEI, and standard SEI + TAU arms, respectively Inclusion criteria: having completed at least 18 months of 24 months of treatment in SEI services, first diagnosis of schizophrenia spectrum disorder (ICD‐10 (international classification of diseases, 10th revision): schizophrenia F20 schizotypal disorder F21 persistent delusional disorders F22 acute and transient psychotic disorders F23 induced delusional disorder F24 schizoaffective disorders F25 other non‐organic psychotic disorders F28 and unspecified non‐organic psychosis F29) Exclusion criteria: patients with an IQ below 70 points
Interventions	Extended SEI (n = 197) consisted of 3.5 additional years of SEI in patients that already underwent at least 1.5 years of SEI components of treatment included assertive community treatment psychoeducational booster social skills training 1:15 caseload Standard SEI + TAU (n = 203) involved the 1.5 years of SEI after which patients would be discharged to a primary care provider or transferred to a standard adult community mental health care
Outcomes	Recovery ‐ used remission as proxy ‐ defined as no global scores exceeding 2 (that is, mild symptoms) on the SAPS and the SANS over the past three months number of psychiatric hospitalisations number of days in psychiatric hospital positive psychotic symptoms score ‐ SAPS (modified) negative psychotic symptoms score ‐ SANS (modified) death by suicide or natural causes general functioning score ‐ PSP In employment or education client satisfaction score ‐ CSQ
Notes	Funding source: Danish Agency for Science and Technology and Innovation. The Capital Region Denmark and the Central Region Denmark funded the clinical part of the trial. Conflicts of Interest: authors supported by the Danish Agency for Science and Technology and Innovation, the Capital Region Denmark, and the Central Region Denmark for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "The randomisation was centralised and computerised with concealed randomisation sequence carried out by the Copenhagen trial unit".
Allocation concealment (selection bias)	Low risk	The randomisation was centralised and computerised with concealed randomisation sequence carried out by the Copenhagen trial unit (CTU). Block sizes ranging between 10 and 6 were concealed to clinicians and investigators
Blinding of participants and personnel (performance bias) All outcomes	High risk	Not blinded. Subjective primary outcome measure but outcome assessors blind to treatment allocation.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Assessors blind to treatment allocation, not involved in patient's care or have access to patients' clinical notes
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Multiple imputation analysis. Participants leaving the study early balanced between groups but there is a high proportion of 26.4% in the extended SEI arm and 30.1% in the SEI + TAU arm.
Selective reporting (reporting bias)	Low risk	Used modification of originally reported primary and secondary outcomes measure (SAPS) not explicitly stated in protocol. However, data collection CRF only included modified measure not full scale, and implicitly stated in protocol through stratification of participants and criteria for remission only included modified measure, therefore original measure never part of analysis plan and not considered as selective reporting.
Other bias	Low risk	None detected

BTPD: Brief and Transient Psychotic Disorder
CBT: cognitive behaviour therapy
CDS: Calgary Depression Scale
CRF:case report form
CSQ: Client Satisfaction Questionnaire
EASY: Early Assessment Service for Young people with psychosis
NEET: not engaged in education and employment or training
PANSS: Positive and Negative Syndrome Scale
PSP: Personal and Social Performance Scale
RCT: randomised controlled trial
RFS: Role Functioning Scale
SANS: Scale for Assessment of Negative Symptoms
SAPS: Scale for Assessment of Positive Symptoms
SD: standard deviation
SEI: specialised early intervention
TAU: treatment as usual