We followed the Meta-analysis of Observational Studies in Epidemiology guidelines (see supplementary table S1 ).10 (link) Search terms regarding exposure to adversity were chosen based on the most widely studied types of traumatic experiences in the psychosis literature and represented overall exposure, physical, emotional and sexual abuse, physical and emotional neglect, bullying, and parental death. A systematic database search from 1906 up to 2011 was performed on PsychINFO, PubMed, EMBASE, and Web of Science using the following search themes: (“child abuse”; “physical abuse”; “sexual abuse”; “psychological abuse”; “emotional abuse”; neglect*; trauma*; advers*; maltreat*; bully*; bullied; victim*; “expressed emotion”; “communication deviance”; “parental loss”; separate*; discrimination) combined with psychosis-related search terms (ie, psychosis; psychoti*; schizo*; hallucinat*; delusion*; paranoi*) using the Boolean operator “and.” Medical Subject Headings (MeSH) were used to further expand the results of the database search, to identify all relevant studies (table 1 and supplementary table S2 ). The present analysis focused exclusively on childhood trauma (defined as sexual abuse, physical abuse, emotional/psychological abuse, neglect, parental death, and bullying). Other psychosocial adversities included in the original search (parental communication deviance, expressed emotion and discrimination) were not eligible for the present analysis.
The following steps were taken to identify all relevant studies and reduce file drawer effects (publication bias due to the likelihood of studies being published depending on the statistical significance of their results): (1) electronic databases were searched for relevant unpublished material (eg, conference articles) from the year 2000 onward; (2) the database search was extended to reports published in Dutch, French, German, Italian, Portuguese, and Spanish; (3) the authors of all eligible reports were contacted and invited to send any relevant unpublished reports (seesupplementary table S3 ); and (4) the reference lists and citations of eligible articles were examined to identify any eligible report not previously located through the database search (forward- and backward tracking of literature).
The following steps were taken to identify all relevant studies and reduce file drawer effects (publication bias due to the likelihood of studies being published depending on the statistical significance of their results): (1) electronic databases were searched for relevant unpublished material (eg, conference articles) from the year 2000 onward; (2) the database search was extended to reports published in Dutch, French, German, Italian, Portuguese, and Spanish; (3) the authors of all eligible reports were contacted and invited to send any relevant unpublished reports (see
