Study Design
Each year,
during the winter months (when seasonal migrants are home), the
Mexican Migration Project randomly samples households in communities
located throughout Mexico. After gathering social, demographic,
and economic information on the household and its members, interviewers
collect basic information on each person's first and last trip
to the United States. From household heads, they compile a year-by-year
history of U.S. migration and administer a detailed series of
questions about the last trip northward, focusing on employment,
earnings, and use of U.S. social services.
Following completion of the Mexican surveys, interviewers journey to destination
areas in the United States to administer identical questionnaires to migrants
from the same communities sampled in Mexico who have settled north of the
border and no longer return home. These surveys are combined with those
conducted in Mexico to generate a representative binational sample. The
data gathered is contained in the Mexican Migration Database and is made
available to the public through this web-site.
Note:
Click here for
a more comprehensive description of the research methodology
employed by the MMP.
Selection of Communities
The
process of selecting communities for the Mexican Migration
has traditionally relied on anthropological methods. Communities
are chosen after a personal reconnaissance of the geographic
area to be studied by the principal investigators. Because
the project initially focused on Western
Mexico, the traditional heartland for migration
to the Untied States, practically all of the earliest communities
had significant indices of out-migration, which could easily
be detected using field interviews and simple observations
of the frequency of new homes, foreign license plates,
currency exchanges, and international courier services.
The
only demographic fact regularly considered was the community’s
sex ratio, which offer general picture of the intensity of
the process of international migration because in Mexico emigration is so heavily male. After
an initial round of fieldwork, investigators compared their
preliminary data with census statistics and formation available
from bibliographic sources. However, the MMP has never explicitly
sought to survey only communities with high rates of out-migration. Investigators
simply seek to corroborate that there is some migration
from the community in question before proceeding. Then
they select four specific locations to represent each of four
levels of urbanization: ranchos,
with fewer than 2,500 inhabitants; pueblos (towns), having
2,500 to 10,000 inhabitants; mid-sized
cities containing 10,000 to 100,000 inhabitants;
and finally, a metropolitan setting, usually a particular
neighborhood within in a state’s capital city or some
other large city..
In
the pueblos and ranchos, investigators conduct a complete census
of dwellings and undertake random selection from the resulting
list. In mid-sized cities and urban metropolises, investigators
generally chose a traditional, well-established neighborhood–one
not dominated by recent rural-urban migrants. As a result,
the urban samples are in reality samples of urban n neighborhoods
or specifically demarcated quarters. In all cases, the neighborhood
must have at least 1,200 enumerated dwellings, from which a
random sample of 200 is taken.
The
methodology of the MMP thus yields results with a high degree
of representativeness at the community level, and in some of
the smaller pueblos and ranchos investigators have been able
to survey every household in the community. Given that
the sample is not targeted to migrants per se, but surveys
the community as a whole, the project needs a fairly large
sample size to generate a significant number of migrants. Traditional
methods of cluster sampling generally survey small numbers
of respondents across a large number of areas, but this generally
yields small numbers of migrants to study an inability to make
generalizations at the community level. For example,
rather than interviewing 20 households in five communities
we interview 100 households in one community, thereby enabling
us to make generalizations about migratory processes at the
community level. If the frequency of migration is 30%,
on average the surveys would contain only six migrants in each
of the five communities, rather than 30 migrants in one community.
At
present we are able to draw upon an index of migratory developed
for municipalities in Mexico’s
National Population Council (CONAPO) based on the 2000 census. This
index provides reliable information about the level of U.S.
migration prevailing at the municipal level and is particularly
useful in identifying new communities of origin for migrants
in new sending states, where heretofore little information
has been available. In sum, after 25 years of field experience,
the MMP continues to use anthropological criteria for selecting
communities, which are then corroborated with available data
from the census and other sources to confirm the existence
of migrants before making the final selection. Until
2000, we lacked access to a valid measure to indicate the intensity
of emigration from specific municipalities and the only measure
indicating migration was the sex ratio.
Weights
Click here for a more comprehensive description about how we calculate and use weights.
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