MASS MIGRATION FROM MEXICO TO THE UNITED STATES: New evidence of the impact of family background

High fertility and large family sizes do not in themselves constitute a significant push factor in the mass migration from Mexico to the United States of the 1990s. That is the main finding of research by Massimiliano Bratti, Simona Fiore and Mariapia Mendola, to be presented at the Royal Economic Society''s annual conference in Brighton in March 2016. Their study finds that gender and birth order have much more influence on whether a young Mexican is likely to move to the United States.

Many people migrate from one country to another because the job opportunities are better – young people can get a better life with their skills. Many scholars thought that migrants tend to come from larger families because of the pressure in having to care for more family members – surprisingly, this study finds no evidence for this.

The research looks at data on teenagers and young adults to find what, if any, effect family has on a person''s chances of migrating. It finds that a mother''s fertility has no effect on migration – instead, birth order is the most important family cause. Older siblings, especially firstborn men, are more likely to emigrate, but having relatively more sisters than brothers reduces this chance (especially for women).

These findings match up with what we know about families in developing countries, where larger families are not necessarily bad for children''s economic outcomes despite efforts by governments to reduce family size. But the evidence suggests that the amount of support parents give to their children''s decision to migrate might matter for family sizes. This is because poorer parents are more likely to need their children to support them, so a better way of dealing with family sizes, migration and old age would be to introduce pensions and insurance.


High fertility and large family sizes do not constitute a push factor in the Mexico-US mass migration of the 1990s. That is the central finding of this empirical study by Massimiliano Bratti, Mariapia Mendola and Simona Fiore.

Labour mobility, especially from poor to rich countries, is one of the most important ways through which young adults can expand their human capital and economic opportunities. Many scholars and observers argue that migrants tend to come more from relatively larger families because of the pressure of the family hierarchy, higher dependency ratio and limited disposable resources, such as land, to support the family members. This study finds no support for this argument.

Mexico went through a demographic boom and transition over the last century, with a birth rate of about seven children per mother in 1970, which, by 2007, had declined to slightly more than two.

Over the same period, the Mexico-US migration wave has swelled, accounting for one third of total US immigration and one tenth of the entire population born in Mexico. Yet, migration patterns in the 1990s differ by age and gender, with a significant fraction being Mexican males migrating in the age between 15 and 30.

In this study, the authors use a rich household-survey dataset providing information on teenagers and young adults to investigate the causal effects of family size and family structure on migration outcomes in Mexico. They focus on the probability of migration of Mexican adolescents and young adults as a function of their birth order, the number of siblings they have, and their composition by age and gender.

In order to identify the causal effect of family size, the researchers make use of variation across mothers in the incidence of virtually random biological fertility (miscarriages) and infertility shocks.

Bratti, Mendola and Fiore find that fertility has no causal impact on migration. The positive correlation between family size and migration disappears when accounting for unobservable determinants of fertility choices correlated with migration.

On the other hand, the opportunities to migrate are significantly different between siblings within the same family (sibling rivalry). Older siblings, especially firstborn males, are more likely to migrate while, conditional on family size, having relatively more brothers than sisters systematically decreases the likelihood to migrate, especially among girls. Firstborn females, for example, are significantly less likely to migrate than firstborn males by three percentage points, which means a reduction in the probability of migration of roughly 60% at the sample average migration rate.

These findings are in line with other recent work showing that large families in developing contexts are not necessarily bad for children''s economic outcomes, but age and gender may matter more.

In terms of policy, understanding the link between fertility and migration is especially relevant today as many governments in developing countries have attempted to curb population growth as a way of increasing average human capital investment and possibly reduce migration, For example, China and India, the world''s two most populous countries, have experimented with different family planning policy to limit family size.

Yet while there is no causal link between fertility and migration, evidence from this study points to the fact that parental investment in their offspring''s migration may matter for lifetime fertility choices. This is so as, in poor contexts, parents are likely to depend on their grown-up children for the provision of care and income, and high migration opportunities can significantly contribute to old-age living arrangements.

Hence, effective population policies and interventions will most likely have little to do with it directly: proper social safety nets (such as old age pensions) or even the development of credit and insurance markets could lead to a reduction in both fertility and migration in developing countries, and perhaps also to less bias against girls.

Family Size, Sibling Rivalry and Migration: Evidence from Mexico