EASY_Extended.

Study characteristics
Methods	Study design: individually‐RCT Duration: 12 months extension of SEI + 12‐month post‐treatment follow‐up. Two‐year duration standard SEI (prior to trial) is followed by one‐year extension of ESEI (in intervention arm), and a one‐year follow‐up. Total SEI plus ESEI duration was three years Setting: community‐based mental health team, Hong Kong Recruitment method: patients who had received two years of the standard EASY programme following their first episode of psychosis
Participants	Diagnosis: the majority were schizophrenia spectrum disorders (84% in extended SEI arm and 80% in SEI + TAU arm) Sample size: 160 participants randomised Age: mean age of onset of psychosis of 20.3 (SD = 3.1) Sex: 50% male and 51% male in extended SEI, and standard SEI + TAU, respectively Inclusion criteria: received 2 years of treatment in the EASY programme following a first episode of psychosis Exclusion criteria: intellectual disability, substance‐induced psychosis, psychotic disorder due to a general medical condition or an inability to speak Cantonese Chinese for the research interview
Interventions	Extended SEI (n = 82) consisted of 1 additional year of SEI in patients that already underwent at least 2 years of SEI components of treatment included phase‐specific case‐management caseload 1:80 relapse prevention psychoeducation SEI + TAU (n = 78) included outpatient medical follow‐up with limited community support
Outcomes	Recovery ‐ used remission as proxy ‐ recovery was defined according to the Remission in Schizophrenia Working Group based on the PANSS criteria of a PANSS score of less than 3 on questions P1 – P3, N1, N4 and N6, and G5 and G9 for six months Disengagement ‐ if participants were no longer attending mental health treatment during the trial follow‐up Admission to psychiatric hospital Number of days in psychiatric hospital General psychotic symptoms score ‐ PANSS Positive psychotic symptoms score ‐ PANSS Negative psychotic symptoms score ‐ PANSS Depressive symptoms score ‐ CDS Death via suicide or natural causes General functioning score ‐ RFS Employment or education status
Notes	Funding source: the study was supported by a grant from the Commissioned Research on Mental Health Policy and Services (SMH‐29) of the Food and Health Bureau, Government of Hong Kong Special Administrative Region Author Conflicts of Interest: EYHC has been a member of the paid advisory board for Otsuka and has received educational grant support from Janssen‐Cilag, Eli Lilly, Sanofi‐Aventis and Otsuka. EHML has been a member of the paid advisory boards for Eli Lilly and AstraZeneca.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computer‐generated allocation sequence. Quote: "An allocation sequence was computer‐generated with a fixed block size of four".
Allocation concealment (selection bias)	Low risk	Randomisation carried out by an independent staff member. Quote: "Randomisation and concealment procedures were conducted by an independent research staff member who was not involved in recruitment, clinical management or research assessment of the study participants"
Blinding of participants and personnel (performance bias) All outcomes	High risk	Not blinded. While the primary outcome measure was subjective, the outcome assessors were blind to treatment allocation.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Research assistant carrying out assessment was masked to allocation group. Quote: "Trained research assistants masked to treatment allocation administered all assessments".
Incomplete outcome data (attrition bias) All outcomes	Low risk	Missing data balanced in numbers across groups (3 lost from extended SEI, 1 from SEI + TAU) with similar reasons for leaving. Intention to treat analysis carried out using a linear mixed model.
Selective reporting (reporting bias)	Low risk	Outcomes reported as in registry
Other bias	Low risk	None detected