Migration psychosis and homicide in Singapore: An 8‐year update

The media and social commentators often suggest an indirect connection among immigration, subsequent development of psychosis, and increased violent crime, especially homicide.1 Linking immigration to a subsequent development of psychosis and risk of violence may have at one time been based on observations linked to the fluidity of certain populations,2 but recent studies call into question these earlier hypotheses.3 Psychiatric research into acts of violence, especially homicide, has been scarce in South East Asia, with the last nation-wide review of homicides in Singapore published in 2006.4 Koh and colleagues looked at 110 accused homicide offenders over 5 years.4 Results suggested an increased vulnerability to homicide in migrant populations due to preexisting but untreated mental disorders. We chose to update the previous estimates due to: (i) our changing understanding of the relationships among homicide, migration, and mental illness3; (ii) the increased prevalence of migration (which has made Singapore the country with the highest proportion of foreign workers in Asia)5; and (iii) the mental health services’ increased focus on delivering community rather than institutionalized care.6 We expected a proportionate increase in migrant representation among offenders because of the increased rate of migration. And, given the additional screening requirements for migration, we expected to see fewer historic risk markers for violence in foreign offenders. We conducted court document file reviews to extract data on all 253 homicide cases from January 2007 to December 2014 to determine the prevalence of mental illness in local and foreign offenders, replicating the 2006 study.4 Our previous study considered data from 110 homicide offenders from 1997 to 2001. The relevant court documents (prison medical records and psychiatric records) of these accused were used to derive information about their demographics, their personal histories, and their psychiatric diagnoses. Ethics approval was obtained from the Institute and from the National Healthcare Group Domain Specific Review Board (NHG DSRB 2015/00476). We compared local and foreign accused via χ2-test (or Fisher's exact test where necessary) or t-test. Where indicated below, we used post-hoc tests of proportion to test differences. We compared current with previous estimates via the same method. Analyses were conducted in Stata 15.0 (StataCorp, College Station, TX, USA). Statistical significance was set at P < 0.05.7 Between January 2007 and December 2014, 253 individuals were charged with homicide in Singapore. This represents a rate of 36 cases per year, up from the rate previously reported of 22 per year. Unlike the previous estimates that noted an 8.3% over-representation of foreigners, the ratio of foreign/local accused matches that of the population with 29% of all accused being foreign. Variables that differentiate local from foreign accused offenders are presented in Table S1 of Appendix S1. Past history of violence and past contact with forensic services were considerably lower in foreigners. Unlike the previous estimate, we found that more foreign offenders were women, suggesting a growing vulnerability to social conditions that lead to homicide. Concerning mental illness, 53% of foreign accused did not have a mental illness, mirroring previous findings (Table 1). However, fewer foreigners appear to have had psychotic disorders. Of note is the growth in substance-related diagnoses, which rose 9% in foreign accused, and 15% in local accused. The links made by the media among homicide, mental illness, and migration appear unsupported in Singapore. While the estimated yearly rate of homicide has increased since the previous study, we have observed lower rates of mental illness, especially psychosis, among the foreign accused. Only one of the 72 foreign accused offenders met criteria for a psychosis-related diagnosis at the material time. While migrant populations now account for a larger portion of Singapore's population,8 their representation among accused homicide offenders has not grown. There is, however, a growing treatment gap in accused homicide offenders, with more meeting criteria for mental illness, but fewer having had previous contact with services, compared to previous estimates. This may point to a need for the implementation of mental health screening. Our findings have several implications for policy, especially if the observed over-representation of women is replicated in the future and if the rate of substance-use-related diagnoses continues to rise. The unexpected increase in the representation of women likely signals a need for more correctional services for women, as well as greater political sensitivity to the challenges faced by this segment of the population. Further research is needed to shed light on the reason for the increased representation of female foreign accused homicide offenders. None of the authors declare financial or professional conflicts of interest. No external funding was required or obtained to complete the study. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.