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Testing Ødegaard's selective migration hypothesis: a longitudinal cohort study of risk factors for non-affective psychotic disorders among prospective emigrants

Published online by Cambridge University Press:  01 August 2014

E. van der Ven ,
C. Dalman ,
S. Wicks ,
P. Allebeck ,
C. Magnusson ,
J. van Os  and
J. P. Selten
E. van der Ven*
Affiliation:
Maastricht University, School for Mental Health and Neuroscience, Maastricht, The Netherlands Rivierduinen Psychiatric Institute, Leiden, The Netherlands
C. Dalman
Affiliation:
Public Health Epidemiology, Department of Public Health Sciences, Karolinska Institutet, Stockholm, Sweden Centre for Epidemiology and Community Medicine, Stockholm County Council, Sweden
S. Wicks
Affiliation:
Public Health Epidemiology, Department of Public Health Sciences, Karolinska Institutet, Stockholm, Sweden Centre for Epidemiology and Community Medicine, Stockholm County Council, Sweden
P. Allebeck
Affiliation:
Social Medicine, Department of Public Health Sciences, Karolinska Institutet, Stockholm, Sweden
C. Magnusson
Affiliation:
Public Health Epidemiology, Department of Public Health Sciences, Karolinska Institutet, Stockholm, Sweden Centre for Epidemiology and Community Medicine, Stockholm County Council, Sweden
J. van Os
Affiliation:
Maastricht University, School for Mental Health and Neuroscience, Maastricht, The Netherlands Department of Psychosis Studies, King's College London, King's Health Partners, Institute of Psychiatry, London, UK
J. P. Selten
Affiliation:
Maastricht University, School for Mental Health and Neuroscience, Maastricht, The Netherlands Rivierduinen Psychiatric Institute, Leiden, The Netherlands
*
*Address for correspondence: E. van der Ven, Rivierduinen Mental Health Institute, GGZ Leiden, Sandifortdreef 19, 2333 ZZ Leiden, The Netherlands. (Email: [email protected])
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Abstract

Background

The selection hypothesis posits that the increased rates of psychosis observed among migrants are due to selective migration of people who are predisposed to develop the disorder. To test this hypothesis, we examined whether risk factors for psychosis are more prevalent among future emigrants.

Method

A cohort of 49 321 Swedish military conscripts was assessed at age 18 years on cannabis use, IQ, psychiatric diagnosis, social adjustment, history of trauma and urbanicity of place of upbringing. Through data linkage we examined whether these exposures predicted emigration out of Sweden. We also calculated the emigrants' hypothetical relative risk compared with non-emigrants for developing a non-affective psychotic disorder.

Results

Low IQ [odds ratio (OR) 0.5, 95% confidence interval (95% CI) 0.3–0.9] and ‘poor social adjustment’ (OR 0.4, 95% CI 0.2–0.8) were significantly less prevalent among prospective emigrants, whereas a history of urban upbringing (OR 2.3, 95% CI 1.4–3.7) was significantly more common. Apart from a non-significant increase in cannabis use among emigrants (OR 1.6, 95% CI 0.8–3.1), there were no major group differences in any other risk factors. Compared to non-emigrants, hypothetical relative risks for developing non-affective psychotic disorder were 0.7 (95% CI 0.4–1.2) and 0.8 (95% CI 0.7–1.0), respectively, for emigrants narrowly and broadly defined.

Conclusions

This study adds to an increasing body of evidence opposing the selection hypothesis.

Keywords

Epidemiologymigrationpsychosisrisk factorselection hypothesis
Type
Original Articles
Information
Psychological Medicine , Volume 45 , Issue 4 , March 2015 , pp. 727 - 734
Copyright
Copyright © Cambridge University Press 2014 

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