Study Design
The data contained in the MMP Database has been gathered using
an approach that borrows from anthropological and sociological research
methods. In particular, the study employs the ethnosurvey approach,
which combines the techniques of ethnographic fieldwork and representative
survey sampling to gather qualitative as well as quantitative data.
The two kinds of empirical data are compared throughout the study
to yield results of greater validity than either an ethnography
or a sample survey could provide alone. This method was designed
to provide a picture of Mexican-US migration that is historically
grounded, ethnographically interpretable, quantitatively accurate,
and rooted in receiving as well as sending areas.
Ethnosurvey Questionnaire
The study's questionnaire follows a semi structured format to generate
an interview schedule that is flexible, unobtrusive and non threatening.
It requires that identical information be obtained for each person,
but question wording and ordering are not fixed. The precise phrasing
and timing of each query is left to the judgment of the interviewer,
depending on circumstances. The gathered information is cross-checked
with local informants to ensure its validity, and a separate ethnographic
study of the community is conducted to provide an independent base
of qualitative information. Go to our Ethnosurvey page to obtain our most recent version.
Interviewing Process
The questionnaires are applied in three phases. In the first phase,
basic social and demographic data are collected from all members
of the household. The interview begins by identifying the household
head and systematically enumerating the spouse and children, beginning
with the oldest. All children of the head are listed on the questionnaire
whether or not they live at home, but if a son or daughter is a
member of another household, this fact is recorded. A child is considered
to be living in a separate household if he or she is married, maintains
a separate house or kitchen, and organizes expenses separately.
After listing the head, spouse, and children, other household members
are identified and their relationship to the head clarified.
A particularly important task in the first phase of the questionnaire
is the identification of people with prior migrant experience in
either the United States or Mexico. For those individuals with migrant
experience the interviewer records the total number of U.S. trips,
as well as information about the first and most recent U.S. trips,
including the year, duration, destination, U.S. occupation, legal
status, and hourly wage. This exercise is then repeated for first
and most recent migrations within Mexico.
The second phase of the ethnosurvey questionnaire compiles a year-by-year
life history for all household heads, including a childbearing history,
a property history, a housing history, a business history, and a
labor history.
The third and final phase of the questionnaire gathers information
about the household head's experiences on his or her most recent
trip to the United States, including the mode of border-crossing,
the kind and number of accompanying relatives, the kind and number
of relatives already present in the United States, the number of
social ties that had been formed with U.S. citizens, English language
ability, job characteristics, and use of U.S. social services.
Data at the community level are gathered as well, at the time of
the survey by the interviewer in charge of the procedure. The sources
for these data have been local informants and the interviewer her/himself.
A form serves as a guide for the task of collecting community level
data. This form is usually referred to as the Community Data Inventory.
Sample Design
A variety of communities have been sampled in order to provide
a basis for comparative study and generalization. These communities
have been chosen to provide a range of different sizes, regions,
ethnic compositions, and economic bases. The sample thus includes
isolated rural towns, large farming communities, small cities, and
very large metropolitan areas; it covers communities in the states
of Aguascalientes, Baja California Norte, Chihuahua, Colima, Durango,
Guanajuato, Guerrero, Hidalgo, Jalisco, México, Michoacán, Morelos, Nayarit,
Nuevo León, Oaxaca, Puebla, San Luis Potosí, Sinaloa,
Tlaxcala, Veracruz, Yucatán, and Zacatecas (see map);
it contains both indigenous and mestizo towns; and it embraces communities
that specialize in mining, fishing, farming, and manufacturing,
as well as those that feature very diversified economies.
Three to five Mexican communities are surveyed each year during the
months of December and January of successive years. The sample size
is generally 200 households unless the community is under 500 residents,
in which case a smaller number of households is interviewed. If
initial fieldwork indicates that U.S. migrants return home in large
numbers during months other than December or January, interviewers
return to the community during those months to gather a portion
of the 200 interviews.
These representative community surveys yield information on where
migrants go in the United States, and during the months of July
and August interviewers travel to those U.S. destinations to gather
non-random samples of 10 to 20 out-migrant households from each
community. The U.S.-based samples thus contain migrants who have
established their households in the United States.
Data Coding and File Construction
After the ethnosurvey questionnaires are completed and revised, data are entered
in Mexico. The entry programs perform initial screening, range checks,
and simple tests for logical consistency. The preliminary files
are then transferred to Princeton University, where additional
data cleaning is performed, numeric codes are assigned to occupations
and places, and the final data sets are assembled. SIX primary
files have been created, each corresponding to a different unit
of analysis: PERS, MIG, MIGOTHER, HOUSE, LIFE and SPOUSE. Data at the community
level have been compiled in the file: COMMUN.
Weights
The MMP database provides community- and sample-specific weights. For each community, you will see a single weight for all the households in the home country sample and another weight for all the households in the US sample.
When working with pooled data from multiple communities, these weights give you the option to adjust your estimates in order to take into account the relative sizes of all the sampling frames. Whether you will need to weight your estimates or not will depend on what your goal is. The document below contains a detailed explanation on our computation of the weights, and suggests criteria to use them or disregard them. For the sake of the example, the text focuses on the MMP71 database, but it applies to the latest release.
Weights |
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MMP and LAMP weights |
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