THE DEMOGRAPHY OF MEXICAN MIGRATION TO THE US

Gordon H. Hanson, UCSD and NBER
Craig McIntosh, UCSD

December 2008

Abstract. In this paper, we use projections for US and Mexican population growth tosimulate Mexico’s future emigration rate, assuming that relative labor demand in the twocountries remains constant. Labor supply pressures for emigration from Mexico peaked in thelate 1990s and are likely to fall in coming years, with the projected emigration rate for labormarket entrants in 2030 being only one third the level for 2000. However, while Mexico’s labor
force growth is slowing, Central America’s is not, meaning that in coming decades Mexico may
face conditions on its southern border similar to what the US has just seen.

The last three decades have been an exceptional period in Mexican migration to theUnited States. As recently as 1970, the share of Mexico’s population living in the US was only
1.5%; by 2005, it had risen to 10.2%. While the flow of labor across the Mexico-US border is
not a new phenomenon, with previous surges occurring in the 1920s and 1950s, persistent massmigration between the countries did not take hold until late in the 20th century.
Among the factors contributing to large scale emigration from Mexico are weak growthin the country’s labor demand and strong growth in its labor supply. After enjoying sustained
economic progress in the 1960s and 1970s, Mexico’s economy stagnated in the 1980s. Repeatedcurrency crises reversed the effects of short-lived expansions, leaving per capita GDP in theearly 2000s more or less unchanged from two decades before. During periods of wage decline in
Mexico, emigration from the country spiked (Gordon Hanson and Antonio Spilimbergo, 1999;
Pia Orrenius and Madeline Zavodny, 2005).
Perhaps less appreciated is that the 1980s were also a period of accelerated growth in
Mexico’s relative labor supply. With the US baby boom peaking in 1960, the number of US
native born individuals coming of working age actually declined in the 1980s. Adding in the
secular increase in US educational attainment, the number of native born American workers withless than a high school education has dropped sharply. In Mexico, high levels of fertility in the
1960s and 1970s meant that two decades hence the country had large numbers of young adults
entering the labor force. While educational attainment has also increased in Mexico, themajority of those born in the country still complete less than 12 years of schooling. The sharp
increase in Mexico-US relative labor supply was concurrent with the stalling of Mexico’s
economy, creating ideal conditions for an emigration surge. In previous work (Hanson and Craig
McIntosh, 2008), we find that temporal variation in labor supply across Mexican states can2account for 30% of the country’s labor exodus between 1975 and 2000.1
Looking forward, the conditions behind recent emigration from Mexico are unlikely to besustained. Whatever happens to labor demand in the country, labor supply growth is converging
to US levels. Between 1965 and 2000, Mexico’s total fertility rate plummeted from 7 to 2.5,
close to the US rate of 2.1. In this paper, we use projections for US and Mexican population
growth to simulate Mexico’s future emigration rate, assuming that relative labor demand in thetwo countries remains constant. Labor supply pressures for emigration from Mexico peaked in
the late 1990s and are likely to fall in coming years, with the projected emigration rate for labormarket entrants in 2030 being only one third the level for 2000. However, while Mexico’s labor
force growth is slowing, Central America’s is not, meaning that in coming decades Mexico may
face conditions on its southern border similar to what the US has just seen.

I. An Empirical Model of Emigration
To model migration from Mexico to the US, we adopt the framework in George Borjas(2006), as extended by Hanson and McIntosh (2008). Labor moves from Mexico to the US in
response to wage differences between the countries, which are determined by relative labor
supply and relative labor demand. There are adjustment costs in moving labor between
countries, such that a 1% wage difference between the US and Mexico induces a fraction σ of the
population to emigrate. When a birth cohort in Mexico comes of working age, the share thatemigrates is an increasing function of the US-Mexico wage differential. As long as a wage gap
between the countries persists, the total emigration rate for a Mexican cohort will rise over time,and may accelerate if there are network effects in US migration.

1

For cross-country evidence on the relationship between demographic structure and international migration, seeHatton and Williamson (2005).

3Given this set up, the equilibrium emigration rate for birth cohort i from Mexican state sin the tth year after it comes of working age (assumed to be 16) can be shown to be:(1)Lmx
X ismxis
mist = β0 + ln us ⎡⎣β1 + β 2 ( t − 1) ⎤⎦ + ln us ⎡⎣β3 + β4 ( t − 1) ⎤⎦ + β5 Z ist ,Li
Xi

where mist is the fraction of the cohort that migrates to the US, Lci is the size of birth cohort i incountry c, X ic is the position of the labor demand curve facing birth cohort i in country c at age
16, and Zist controls for other labor market shocks. Interactions between initial labor market
conditions and time since a cohort entered the labor force reflect the dynamics of wage
adjustment in the two countries in response to migration and the effects of migration networks.
Because the estimated interactions are small, in our simulation exercises we focus on the main
effects of initial labor market conditions on emigration. Since the relevant US labor market formost Mexican migrants is low skilled work, it would be natural to measure Lusi as the number of
US native born in cohort i that have not completed high school. In Hanson and McIntosh (2008)
we take this approach, instrumenting for the number of US high school dropouts with the total
size of the relevant US birth cohort. The estimated value of β1 is 0.14 (and highly statisticallysignificant), implying that for every 10% increase in the relative size of a Mexican birth cohort,
an extra 1.4% of the cohort would emigrate each decade.2
We use estimation results for equation (1) to simulate the effects of projected population
growth in the US and Mexico on future Mexican emigration. Because our focus is on how labor
supply affects emigration, we shut down the effects of labor demand (and any feedback effects
from labor supply to labor demand that would occur if population growth affects capital2

The regression is run using data on emigration rates for three-year birth cohorts by Mexican state at ten year
intervals for the period 1960 to 2000. Other controls in the regression include log state per capita GDP relative to
US per capita GDP in the year the cohort turned 16, the log change in state per capita GDP relative to US per capita
GDP in the most recent ten year period, and dummies for gender, age group, 10-year birth cohort, and year.

4accumulation or technological progress). The simulations are thus not a forecast of the future
emigration rate. Rather, they allow relative comparisons across time of the effect of the U.S.Mexican labor supply ratio on migration, holding relative labor demand constant across periods.

II. Projecting Labor Supply Growth in Mexico and the US
To perform the simulations, we need projections for future population growth in the US
and Mexico. For the US, we use projections from the US Bureau of the Census (2008), which
predicts the number of births in the US, accounting for how immigration affects the populationof mothers of birthing age. For Mexico, we combine demographic projections for fertility with
our own projections of the number of women of birthing age that remain in the country.
Mexican fertility rates are from Rodolfo Tuiran, Virgilio Partida, Octavio Mojarro, and Elena
Zuniga (2002), who forecast age-specific fertility in Mexico, disaggregated by state, birth cohort,and year through 2030. Their projections imply Mexican fertility will continue to fall, dipping
below the replacement level needed to keep population stable by 2020. Below, we discuss how
emigration could affect fertility trends by changing the incentive of mothers to have children.
To project the number of women of birthing age in Mexico, we begin by counting thenumber of women of each age and state in the 2000 Mexican census and then apply age-specificannual female emigration rates over the 1960 to 2000 period to obtain the number of women ofeach age remaining in Mexico through 2030. For our purposes, using emigration rates averaged
over 1960-2000 is a conservative approach, as it implies a higher labor supply in Mexico (andtherefore a smaller change in future emigration rates) than would obtain were we to use
emigration rates for a more recent period, such as 1990-2000. Combining the Tuiran et al.
(2002) fertility forecasts with our population projections, we predict the number of children thatwill be born in each Mexican state and each year to women who were in Mexico as of 2000. As
5

of 2016, girls whose births were simulated become fertile and so begin themselves to add to birthcohort sizes. We assume a commensurate fraction of these girls will emigrate, taking them outof the pool of prospective birth mothers in Mexico.3
The resulting forecasts of births in the US and Mexico are in Figure 1. The series until
2006 reflect actual births, as reported in World Development Indicators. Over 1960-1980, it isevident that the Mexico-US ratio of number of births increased dramatically, rising from 0.35 to
0.66. This surge in relative Mexican births in the 1960s and 1970s contributed to a sharp
increase in the relative number of individuals coming of working age in Mexico in the 1980s and1990s. These are the generations of Mexicans that have migrated to the US in large numbers.
The era of rising relative Mexican labor supply has already come to an end. By1980, therelative number of births in Mexico had stopped rising. The combination of falling fertility in
Mexico, emigration from Mexico, and immigration in the US (from Mexico and elsewhere), hascaused the number of births to flatten out in Mexico and to rise in the US. After 2010, thisprocess accelerates. The number of births in the US continues to grow (as future immigration
contributes to population growth) and the number of births in Mexico stays relatively constant.
Of course, what matters for the incentive to migrate to the US is not Mexico’s relative total labor
supply but its relative supply of comparably skilled workers. Here, too, we see a reversal in thegrowth in relative Mexican supply. The ratio of 20 year olds born in Mexico to 20 year oldnative born high school dropouts in the US rose from 1.2 in 1960 to 3.8 in 1980 and to 5.1 in1990 but then fell to 5.0 in 2000.
3

In order to simulate these children of children, we first divide the number of children born in each state/year by
two to get the number of girls of each age, and then adjust for emigration by these girls’ mothers since the girls wereborn. This gives the number of children born in each state from 2016-2030 to children of those who were in the
country as of 2000. We sum the number of girls for each year 2001-2030 (both observed in 2000 and simulated
after 2015) within each age category and then multiply this female population times the year- and age-specificfertility rates. This gives the number of children born to women of each age category for each year. Finally, we
sum across age categories to get the number of children born in each state/year (where we smooth state-level cohort
sizes across birthyear to adjust for lumpiness resulting from the five-year fertility bins used by Tuiran et al. (2002)).

6

Figure 1: Projected Population Growth in the US and Mexico

12

Million Births
345

Total Birth Cohort Sizes

1960

1980

2000
Birth Year
MX, Actual
MX, Projected

2020

2040

US, Actual
US, Projected

Source: WDI, US Census Dept, MX projections by authors

Much of the slowing in the number of births in Mexico is due to the dramatic fall in the
country’s fertility rates. Mexico’s experience is similar to other middle income countries, whichhave seen fertility decline as their populations have urbanized, become more educated, andincorporated women in to the labor force in larger numbers. The countries of Central America
that lie just to the south of Mexico have not experienced fertility declines anywhere near as large
as in Mexico and continue to have rapid population growth. Figure 2 plots the number of births
in Mexico and the number of births in four Central American countries (El Salvador, Guatemala,Honduras, Nicaragua—which are the countries in the region with significant migration to theUS), each relative to the US. In both Mexico and Central America, the number of births relative
to the US rose sharply in the 1960s and 1970s. Mexico reached its peak in the mid 1970s and7then began its steady decline. In Central America, however, relative births increased by 80%
between 1960 and 1980 and then remained flat for the next 30 years. While relative labor supply
growth in Mexico has slowed, relative labor supply growth in Central America has not. Births in
the region have grown sharply relative to Mexico, meaning that in ensuing years Mexico may
experience demographic pressures for immigration on its southern border, as large cohorts innearby countries come of working age. The large increases in education among poor Mexicans
brought about by subsidized schooling programs (such as Progresa/Oportunidades) may further
enhance Mexico’s attractiveness as a destination for future Central American migrants.

Figure 2: Relative Population Growth in Central America, Mexico, and the US

Ratio of Births per Year by Country

1

1.2

1.4

1.6

1.8

2

1960=1

1960

1970

1980

1990

2000

2010

year
Mexico/USA

Central America/USA

Source: WDI

8

III. Projecting Migration from Mexico to the US
All else equal, the reversal in Mexico’s relative labor supply growth would ease pressuresfor emigration from the country. To project how large the change in emigration coming fromchanges in labor supply is likely to be, we use our population projections to simulate the share ofeach birth cohort in Mexico that emigrates to the US. For the period up to 2006, we use actual
births as recorded in World Development Indicators; for 2007-2030, we use our population
projections. We take the series of Mexico-US relative labor supply and apply our dynamic
migration model in equation (1) to calculate the total fraction of each cohort that migrates to the
US over its prime migration years. Obviously, over long time periods labor demand in the twocountries could change dramatically. Since there are no reliable forecasts of how labor demandis likely to evolve, we neutralize its effects by assuming that the position of the US-Mexico
relative labor demand curve remains constant over time. This implies we can only simulate
emigration relative to some base cohort, which we choose to be 1960.
Figure 3 presents the simulation results, in which emigration rates are smoothed overtime. The plot shows the total fraction of an age cohort that migrates to the US between ages 16
and 40. The horizontal axis indicates the year in which a cohort turns 16, such that the first year
shown is 1976, when the 1960 birth cohort comes of working age. Initially, the simulated
emigration rate rises sharply, peaking in 1995, for the cohort born in 1979. For the cohort
entering the labor market in that year, labor supply pressures imply a life time emigration rate
22% higher than for 1976 entrants. Since relative births in Mexico peak in the late 1970s, labor
supply pressures on emigration weaken for age cohorts entering the labor force after the 1990s.
The decline is modest at first, such that for labor market entrants in 2010 the emigration rate isstill 14% higher than for 1976 entrants. After 2010, the decline continues, falling to 9% in 20209and 7% in 2030, one third of the level in the late 1990s.
Figure 3: Labor Supply Pressures for Mexican Migration to the US

Simulated Cohort-Level Migration
Percent of cohort that eventually migrates
0
5
10
15
20

Relative to 1960 birth cohort

1980

2000

2020
Year cohort turns 16

2040

2060

Effect in differences from the 1960 birth cohort, which turns 16 in 1976

The size of Mexican cohorts coming of working age in the 1990s and 2000s createdunprecedented labor supply pressures for emigration from the country. Between the rapid
decline in Mexican fertility and the immigration-induced population growth in the US, relativelabor supply pressures are already easing and will likely relax considerably in coming decades.
While labor supply is by no means the only factor behind labor outflows from Mexico, the US
and Mexico have clearly passed through a period that is unlikely to be repeated. Given thatbirths in the Central American region appear likely to remain high relative to the US and to rise
relative to Mexico, one would expect continued migration from Central America to the US andan acceleration of migration to Mexico. Since the early days of the Spanish conquest, Mexico
has not experienced a significant immigration surge. Labor inflows into the country appear
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likely to increase. Substantial numbers of Central Americans already cross into southern
Mexico, on their way to the US.
The simulation in Figure 3 only considers labor supply pressures on Mexican migration
to the US. Ignoring labor demand is a serious liability in forecasting migration. Mexico’s
capacity to sustain high rates of economic growth matters hugely for the incentive of its citizens
to leave. The simulations also ignore feedback effects from labor supply to labor demand. The
size of an economy, in part determined by its population, could affect productivity and wages if
scale economies are important. Consequently, the growing size of the US economy relative to
Mexico could slow convergence in Mexican income levels. Our simulation also ignores crosscohort network effects, which may similarly work to slow the decline in migration.
Other qualifications of the simulation relate to the behavior of fertility. It appears that
fertility in Mexico is following the pattern of Catholic countries in southern Europe, which haveseen precipitous declines in birth rates to below replacement levels. Reasons for this decline are
not fully understood. Obviously, if this fertility decline in Mexico reverses itself the easing of
emigration pressures in the country could be more modest. Another issue is whether migration
itself affects fertility. Part of the fall in Mexican birth rates could be a result of increased
opportunities for young women to move to the US. The prospect of living in the US may induce
women to have fewer children, as a result of Becker type effects in which expected higher future
income induces women to choose to have fewer children but invest more in each one.
Additionally, moving from one country to another is disruptive, possibly causing women todelay fertility until they complete their move abroad.
To examine the correlation between migration and fertility, Figure 4 uses data from the2000 US and Mexican censuses to plot fertility for migrant women before and after they move to11the US, relative to the fertility for women who do not migrate. The figure is constructed from a
regression of the 0-1 outcome of giving birth in a given year for a sample of migrant andnonmigrant women (where fertility panels are based on the age of own children in a woman’s
household). The regressors include age, education, year, and leads and lags on dummies forwhether a women migrates to the US in a given year. In the years leading up to migration,
fertility is depressed for future migrants, reflecting the disruptive effects of migration on fertility
and long-run differences in fertility associated with being a migrant. Migrant fertility spikes inthe second year following the move to the US, as women make up for delayed fertility in the premigration period.4 The post-migration fertility spike could also reflect the desire to have a childin the United States. While Figure 4 is purely descriptive, it does suggest that fertility andmigration are related. The subject merits further study.
Figure 4: Fertility of Migrant Women from Mexico before and after Migration

Deviations from Normal Fertility around Migration to the U.S.

-.05

Probability of Birth per Year
0.05

Whole Mexican-born cohort, 2000 US & MX Censuses

Pre-Migration
-5

-4

-3

-2

Post-Migration-1
0
1
Leads/Lags of Migration

2

3

4

5

Coefficients from regression using age, year, and education category fixed effects.

4

Using fixed effects to control for age, year, and education, women who migrate to the U.S. have only very slightly
lower overall fertility than their counterparts who remain in Mexico (the lifetime probability of a birth in any given
year is .7% lower for migrants, relative to a sample average of 7.55%). This relatively small decrease is a composite
of fertility which 1.8% per year lower than the counterfactual prior to arrival in the U.S. and 2.7% higher thereafter.

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IV. Discussion
The flow of individuals from Mexico to the US over the last three decades ranks among
the most significant migration episodes in the histories of the two countries. The exodus from
Mexico appears to have had a strong demographic component. Mexico’s delayed fertility
decline, combined with the US baby bust, amounted to a large positive shock to Mexico’s
relative labor supply. That shock appears to be subsiding. In the future it is Central America andnot Mexico whose demographic structure makes an emigration surge most likely.

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References
Borjas, George J. “Native Internal Migration and the Labor Market Impact of Immigration,”
Journal of Human Resources 41 (Spring 2006): 221-258.
Hanson, Gordon H., and Craig McIntosh. 2008. “The Great Mexican Emigration.” Review of
Economics and Statistics, forthcoming.
Hanson, Gordon H., and Antonio Spilimbergo. 1999. "Illegal Immigration, Border Enforcement
and Relative Wages: Evidence from Apprehensions at the U.S.-Mexico Border," American
Economic Review, 89: 1337-57.
Hatton, Timothy J. and Jeffrey G. Williamson. 2005. “What Fundamentals Drive World
Migration?” In. George J. Borjas and Jeff Crisp, eds., Poverty, International Migration, andAsylum, New York: MacMillan.
Orrenius, Pia M. and Madeline Zavodny. 2005. “Self-Selection among Undocumented
Immigrants from Mexico.” Journal of Development Economics, 78(1): 215-240.
Tuiran, Rodolfo, Virgilio Partida, Octavio Mojarro, and Elena Zuniga. 2002. “Fertility in
Mexico: Trends and Forecast.”. Report of the United Nations Population Division.
US Bureau of the Census. 2008. “Projected Births by Sex, Race, and Hispanic Origin for theUnited States: July 1, 2000 to June 30, 2050,” http://www.census.gov/population/www/projections/downloadablefiles.html.

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