Tarrier 1999.

Methods	Allocation: randomised Blinding: assessor Location: National Health Service trusts in Greater Manchester Lenght of follow‐up: 24 months
Participants	Diagnosis: schizophrenia, schizoaffective psychosis, delusional disorder (DSM‐III R) N = 87 Sex: 69 M, 18 F Age: mean ˜ 39 years, SD ˜ 11 years Included: length of illness: median ˜ 11 years; experiencing psychotic symptoms (i.e. hallucinations or delusions) for at least six months which did not appear to be responding further to medication; no evidence of organic pathology which could have explained the psychopathology; ages 16 ‐ 65 years; receiving regular and stable antipsychotic medication Excluded: not reported
Interventions	1. CBT group*: N = 33 Content: coping strategy enhancement, training in problem‐solving, strategies to reduce relapse Delivered by: three experienced clinical psychologists and followed a protocol manual Frequency: six hourly sessions, each of which were followed by two summary sessions. Sessions were carried out twice a week and 20 sessions of treatment were carried out over ten weeks. Four booster sessions were given once a month for four months. Treatment duration: 10 weeks 2. Standard care group: N = 28 Content: standard psychiatric management with medication, monitoring outpatient follow‐up and care programme approach Delivered by: not reported Frequency: not reported Treatment duration: 10 weeks
Outcomes	Global state: relapse Mental state: clinically important change (no improvement)**, negative symptoms (SANS) Adverse event: death (any cause) Satisfaction with treatment: leaving the study early Unable to use: Mental state: positive symptoms ‐ (log transformed data) calculated by combining PSE and BPRS scores (data not in the format suitable for analysis and we were unable to convert it)
Notes	*Participants in the CBT group also received the standard care intervention. **defined as not achieved 50% improvement in psychotic symptoms in both severity and number of symptoms We did not use the data from a third arm where the intervention was supportive counselling plus standard care (n = 26).
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "...generated by the Institute for Medical Biometry using a computerized algorithm and was stored by CenTrial." (p.S102) Comments: The investigators described a random component in the sequence generation process.
Allocation concealment (selection bias)	Low risk	Quote: "...generated by the Institute for Medical Biometry using a computerized algorithm and was stored by CenTrial." (p.S102) Comments: The allocation assignment were conducted centrally.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Quote: "The therapist then gives the information about treatment allocation to the patient." (p.S102) Comments: Participants and therapists knew the allocation assignment.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "...assessor blind regarding the study condition..." "...the result of the randomisation only to the therapist in order to keep the assessor blind regarding the study condition." (p.S102) Comments: blinding of outcome assessment ensured
Incomplete outcome data (attrition bias) All outcomes	Low risk	Comments: 26 participants dropped out from the trial at 2‐year follow‐up, however, the intention‐to‐treat sample included all randomised participants.
Selective reporting (reporting bias)	Low risk	Comments: All measured outcome were reported.
Other bias	Low risk	Funding source: This study was funded publicly by the German Research Foundation (Deutsche Forschungsgemeinschaft, grants Kl 1179/2‐1 and Kl 1179/3‐1). Comments: none obvious