Hypothesis	Description	Dominant narrative	Quality of evidence (e.g.s)
Social adversities	Pre-, during or post-migratory stressors increase risk, particularly in childhood & adolescence	Accepted	Strong (Price et al., 2018; Morgan et al., 2007, 2008; Hollander et al., 2016)
Sociodemographic differences	Confounding by age, sex or socioeconomic status	Refuted	Strong (Kirkbride et al., 2008; Kirkbride et al., 2017)
Selection effects	People with liability to psychosis more likely to migrate	Refuted	Strong (Ødegaard 1932; Selten et al., 2002; van der Ven et al., 2015)
Misdiagnosis	Raised rates in BME groups due to racial bias in clinical diagnoses or culturally insensitive diagnostic tools	Refuted	Indirect (Lewis et al., 1990; Hickling et al., 1999; Fearon et al., 2006; Heuvelman et al., 2018)
Infections, obstetric complications, substance use	Greater exposure to these risk factors confound the association between psychosis risk and BME status	Refuted	Limited (Hutchinson et al., 1997) / indirect (Sandwijk et al., 1995; Coulthard et al., 2002; Veen et al., 2002; Sharp and Budd 2003)
Higher rates in county of origin	Higher background rate in other countries mean this is not a migration / BME effect per se	Refuted	Limited to Caribbean (Hickling and Rodgers-Johnson, 1995; Bhugra et al., 1996; Mahy et al., 1999)
Novel hypotheses	Mechanisms through exposure to social or other early-life adversities (i.e. substance use, obstetric complications, infections) impact psychosis mediated via cognitive impairments	Untested	Untested

Legend: Main hypotheses to explain elevated psychosis risk in migrants and their descendants. The current evidence most consistently supports a social adversities hypothesis, while sociodemographic and selection effects have been refuted on the basis of reasonable evidence. Other hypotheses have been refuted, but the evidence base to do so is indirect or limited (yellow and red boxes, right hand column), suggesting this may be premature. Novel hypotheses require investigation. BME: black and minority ethnic.