Migration and mental health: Evidence from a natural experiment

Abstract

People migrate to improve their well-being. Yet a large literature suggests that migration can be a stressful process, with potentially negative impacts on mental health. However, to truly understand the effect of migration one must compare the mental health of migrants to what their mental health would be had they stayed in their home country. The existing literature is not able to do this. New Zealand allows a quota of Tongans to immigrate each year with a random ballot used to choose amongst the excess number of applicants. Experimental estimates of the mental health effects of migration are obtained by comparing the mental health of migrants who were successful applicants in the random ballot to the mental health of those who applied to migrate under the quota, but whose names were not drawn. Migration is found to lead to improvements in mental health, particularly for women and those with poor mental health.

Introduction

People migrate to improve their well-being. Economic migrants moving from a developing to a developed country will generally experience large gains in material well-being as they take advantage of higher wages abroad. However, the effects of migration on other dimensions of well-being are less clear. In particular, the process of moving from one cultural setting to another can be a very stressful process, with potentially negative impacts on mental health (Bhugra and Jones, 2001). In fact, the World Health Organization (2001, p.13) goes as far to claim “usually migration does not bring improved social well-being; rather…it often results in…exposing migrants to social stress and increased risk of mental disorders”. To the extent that these mental health changes reduce the net benefits of migration they are of potential interest to economists, especially because there are strong economic arguments for increasing international migration (World Bank, 2005).

However, migration also has a number of effects that may improve mental health. Although recent evidence suggests there is little association between income levels and mental health in developing countries (Das et al., 2007), it is argued that immigrants may experience a deep sense of fulfillment in the short-term by using their new-found wealth to contribute to their extended family, village and church at home (Foliaki, 1997). Migrants may also experience mental health improvements from a change in cultural setting, which allows them to shed the burden of social restrictions that caused them to be anxious or depressed in their home countries.

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. However, the existing literature is not able to do this. The majority of studies compare the mental health of immigrants to those of natives.¹ Such comparisons take no account of any pre-existing differences between immigrants from developing countries and natives in these developed countries.² While a few studies have made comparisons between movers and stayers from the same country (Odegaard, 1932, Maveras and Bebbington, 1988), these studies are also unable to control for the potential selection bias that will occur if unobserved characteristics which increase the propensity to migrate are also associated with either higher or lower risks of mental health disorders.

The direction of this bias is unclear since mental illnesses may lead to restlessness and hence make individuals more likely to migrate, but on the other hand, since long-distance migration is a complicated event, individuals with worse mental health may not be able to handle the processes needed to emigrate (Bhugra, 2004b). VanLandingham and Fu (2007) is the only paper we know of which attempts to deal with this selection, by comparing Vietnamese immigrants in New Orleans to never-leavers in Vietnam and to returnees in Vietnam who initially made it to a country of first asylum but were then repatriated because they could not show a bona fide risk of persecution in Vietnam. While the returnees provide a comparison group in Vietnam of individuals who also wished to migrate, forced repatriation is unlikely to be a random event and likely has its own direct impact on mental health, thus this group provides a less than ideal control group.

This paper overcomes the selection problems affecting these previous studies by examining Tongans who migrate to New Zealand through the pacific access category (PAC). The PAC allows an annual quota of Tongans to migrate to New Zealand, additional to those approved through other migration categories such as skilled migrants and family streams. Many more applications are received than the quota allows, so a ballot is used to randomly select from among the registrations. A unique survey conducted by the authors in both Tonga and New Zealand 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 ballot to the mental health of those who applied to migrate under the quota, but whose names were not drawn. We are also able to compare the mental health of applicants to this migration program to that of non-applicants, examining the role of selection.

Our measure of mental health is the MHI-5 of Veit et al. (1983), a measure of mental health for the general population, which is useful for detecting depression, anxiety, and general affective disorders. Our results show that despite being positively selected in terms of education, Tongans with worse mental health are more likely to apply to migrate to New Zealand. We find that there are large and significant positive effects of migration on mental well-being. We also extend on the current literature, by allowing migration to have non-uniform impacts on mental health and find that migration has larger impacts on women and on individuals with poor mental health. Thus, rather than there being a mental health cost offsetting some of the economic gains from migration in an overall welfare assessment, these results suggest that migration brings positive benefits beyond economic gains.

Public and policy discussions about migration often express significant concern about possible negative social and mental health effects of migration on the migrants, with little hard evidence. Our paper provides the first cleanly identified estimate of the short-term impact of migration on mental health in any context, showing that, at least for Tongans moving to New Zealand, migration is also accompanied by mental health gains. The natural question which arises is then how generalizable these results are to other settings. There are a variety of types of migration, including permanent migration for work, refugees, political asylees, seasonal workers, and forced migrants, and it seems unlikely the mental health effects will be the same for all groups.

Our study concerns the short-term impact of individuals migrating for work with their immediate family from a developing to a much richer developed country. This is one of the most common forms of migration worldwide. Moreover, Tongan migrants are similar in several important respects to the average developing country emigrant moving to work in a rich country. They work in jobs such as construction, cleaning, and retail services frequented by immigrants worldwide. The average Tongan in our sample has 11.7 years of education, compared to 11.0 years for the average 18–45-year-old new immigrant in the US, and Tongans exhibit a similar degree of positive selection on schooling as found among Mexican migrants moving to the US. As such, the results of this study may well generalize to other developing country economic migrants.