WPS4138

# **Migration and Mental Health: Evidence from a Natural Experiment**<sup>**1**</sup>

Steven Stillman, _Motu Economic and Public Policy Research*_ David McKenzie, _Development Research Group, The World Bank_ John Gibson, _University of Canterbury_

# **Abstract**

People migrate to improve their well-being, whether through an expansion of economic and social opportunities or a reduction in persecution. Yet a large literature suggests that migration can be a very stressful process, with potentially negative impacts on mental health reducing the net benefits of migration. However, to truly understand the effect of migration on mental health one must compare the mental health of migrants to what their mental health would have been had they stayed in their home country. The existing literature is not able to do this and typically settles for comparing the mental health of migrants to that of natives in the destination country, which takes no account of any pre-existing differences between these groups. This paper overcomes the selection problems affecting previous studies of the effect of migration on mental health by examining a migrant lottery program. New Zealand allows a quota of Tongans to immigrate each year with a lottery used to choose amongst the excess number of applicants. A unique survey conducted by the authors in these two countries allows experimental estimates of the mental health effects of migration to be obtained by comparing the mental health of migrants who were successful applicants in the lottery to the mental health of those who applied to migrate under the quota, but whose names were not drawn in the lottery. Migration is found to lead to improvements in mental health, particularly for women and those with poor mental health in their home country.

Keywords: Migration, Mental Health, Natural Experiment JEL codes: J61, I12, F22 World Bank Policy Research Working Paper 4138, February 2007 _The Policy Research Working Paper Series disseminates the findings of work in progress to encourage the exchange of ideas about development issues. An objective of the series is to get the findings out quickly, even if the presentations are less than fully polished. The papers carry the names of the authors and should be cited accordingly. The findings, interpretations, and conclusions expressed in this paper are entirely those of the authors. They do not necessarily represent the view of the World Bank, its Executive Directors, or the countries they represent. Policy Research Working Papers are available online at http://econ.worldbank.org._ 1 We thank the Government of the Kingdom of Tonga for permission to conduct the survey there, the New Zealand Department of Labour Immigration Services for providing the sampling frame, Halahingano Rohorua and her assistants for excellent work conducting the survey, and most especially the survey respondents. Mary Adams and participants at the PAA conference provided helpful comments. Financial support from the World Bank, Stanford University, the Waikato Management School and Marsden Fund grant UOC0504 is gratefully acknowledged. The study was approved by the multi-region ethics committee of the New Zealand Ministry of Health. The views expressed here are those of the authors alone and do not necessarily reflect the opinions of the World Bank, the New Zealand Department of Labour, or the Government of Tonga.

* Corresponding author: Email: stillman@motu.org.nz. Address: Motu Economic and Public Policy Research, Level 1, 93 Cuba St., Po Box 24390, Wellington, New Zealand. Phone: 64-4-939-4250 , Fax 644-939-4251.