Methods	Allocation: random, computer-generated randomisation. Blindness: double, identical capsules. Duration: 26 weeks. Design: parallel. Location: multicentre.
Participants	Diagnosis: (DSM-IV) schizophrenia (n=230), schizoaffective disorder (n=116), prominent negative symptoms. N=346. Gender: 228 M, 118 F. Age: mean olanzapine=41.67 years, mean quetiapine=40.45 years. History: duration ill mean olanzapine=17.57 years, quetiapine=17.78 years, age at onset mean olanzapine=24.16 years, quetiapine=22.59 years. Setting: outpatient.
Interventions	Olanzapine flexible dose. Allowed dose range: 10-20 mg/day. Mean dose: 15.6 mg/day. N=171. Quetiapine flexible dose. Allowed dose range: 300-700 mg/day. Mean dose: 455.8 mg/day. N=175
Outcomes	Leaving the study early: any reason, adverse events, inefficacy. Mental State: PANSS total score, PANSS positive subscore, PANSS negative subscore, SANS total score, depression (Calgary Depression Scale). General functioning: GAF, Case Manager Rating Scale, Patient Functioning Rating Scale. Quality of life: QLS total score. Adverse effects: Sedation, weight gain, laboratory (hematology, uric acid) Unable to use- Leukopenia: no useable data. Use of antiparkinson medication: no data.
Notes
Risk of bias
Item	Authors’ judgement	Description
Adequate sequence generation?	Yes	Random, computer-generated randomisation.
Allocation concealment?	Unclear	No further details.
Blinding? Subjective outcomes	Unclear	Double, identical capsules. Whether blinding was successful has not been examined, but both compounds differ quite substantially in side effects. This can be a problem for blinding
Blinding? Objective outcomes	Yes	Objective outcomes such as laboratory measures or death are unlikely to have been much affected by problems of blinding
Incomplete outcome data addressed? All outcomes	No	The overall attrition was very high (54.9%). The last-observation-carried-forward method was used to account for people leaving the study early. It assumes that a participant who discontinued the study would not have had a change of his condition if he had remained in the study. This assumption can obviously be wrong
Free of selective reporting?	No	The numbers of participants who received antiparkinson medication or who had leukopenia were not indicated
Free of other bias?	No	The study was sponsored by the manufacturer of olanzapine.