Options for Estimating Illegal Entries at the U.S.-Mexico Border (2013) / Chapter Skim
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5 Administrative Data on Undocumented Migration Across U.S. Borders
5 Administrative Data on Undocumented Migration Across U.S. Borders
Pages 73-92
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From page 73... ...
interior against illegal immigration, DHS records the number of undocumented migrants it apprehends, the disposition of these migrants, and the resources it devotes to enforcement activities. The relevant administrative data come in three primary forms: apprehensions data collected by the U.S.
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From page 74... ...
cannot, unfortunately, solve the problem about the lack of direct information on the number individuals who elude capture and enter the United States successfully. While administrative data have limitations, they could still offer potential insights into unauthorized migration flows if they were combined with other data sources.
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From page 75... ...
Table 5-1 is a partial list of the variables contained in the ENFORCE database, in which USBP, OFO, and ICE apprehensions data are recorded. Individual USBP apprehension records contain demographic information on the person apprehended, including gender, date of birth, country of origin, and (if a Mexican national)
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From page 76... ...
USBP asserts that it enters information into its database on nearly all current apprehended migrants. Additional information in USBP apprehensions data describes: • Arrest method.
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From page 77... ...
The re-apprehension of individuals provides information that can, in theory, be used to make inferences about the size of the unauthorized population entering the United States successfully. Of apprehensions of Mexican men over the period from 1999 to 2009, approximately threefifths were of individuals who were apprehended only once, one-fifth are of individuals who were apprehended twice over the period, and one-fifth are of individuals who were apprehended three or more times (Borger et el., in press)
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From page 78... ...
Previous uses of apprehensions data to estimate unauthorized migration flows, such as the analyses by Espenshade (1995b) and by Massey and Singer (1995)
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From page 79... ...
A second approach in the use of apprehensions data is to make assumptions about the stochastic process governing apprehensions, generalizing the repeated-trials method developed by Espenshade (1995b)
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From page 80... ...
The systematic collection of data on smuggling prices would expand the options available to DHS for analyzing the behavior of undocumented migration at the U.S.–Mexico border. Frequency of Apprehension Frequencies Analysis An alternative approach for using apprehensions data to estimate the number of individuals crossing the border successfully is to impose assumptions about the underlying stochastic process that governs attempts to cross the border.
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From page 81... ...
.1 To provide an example of how one could use data on apprehensions, Figure 5-1 shows the number of times individuals surveyed in EMIF-N report being apprehended in a given series of attempts to cross the U.S.– Mexico border. The length of the time window used to define apprehensions for a single crossing episode is an important issue.
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From page 82... ...
The absence of notable regional variation in the zero apprehensions category suggests that, despite large cross-sector differences in the scale of enforcement activities, the probability of apprehension may be stable across regions. It would have been preferable to perform the analyses represented in Figures 5-1 and 5-2 using ENFORCE data.
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From page 83... ...
F igure 5-2 of individuals apprehended, whereas EMIF-N only covers those individuals questioned by survey enumerators, whose choice of survey zones and points to find individuals being returned to Mexico after apprehension may intro duce unknown sources of bias into the sample. Of course, both ENFORCE and EMIF-N are subject to the limitation that the population of individuals who are apprehended once but not seen again includes both those who, on their subsequent attempt, cross into the United States successfully and those who, after the initial apprehension, become discouraged and return home to Mexico.
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From page 84... ...
Such changes may indicate that apprehension probabilities are responsive to changes in border enforcement (e.g., the zero-apprehensions category expands because more individuals are being caught) or that the composition of border crossers is responsive to changes in border enforcement (e.g., the zero-apprehensions category expands because more-determined crossers account for a higher fraction of those crossing)
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From page 85... ...
/a. The Conway-Maxwell-Poisson is a variant of the Poisson distribution that allows over-dispersion (like a negative binomial distribution)
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From page 86... ...
The negative binomial, geometric, and Conway Maxwell-Poisson distributions all fit the observed counts closely -- indeed, the lines overlap so that the separate colors are not visible. The Poisson 1.0 Observed Conway-Maxwell Poisson fit Poisson fit Geometric fit 0.8 0.74 0.74 0.75 Negative binomial fit Probability of n Apprehensions 0.6 0.54 0.4 0.2 0 0 1 2 3 4 5 6 Number of Apprehensions, n FIGURE 5-3 Fits of naïve apprehensions models for 2009.
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From page 87... ...
However, conversations with representatives from DHS suggest that the linkages between the apprehensions records controlled by USBP, OFO, and ICE in the ENFORCE database are limited to uses that relate specifically to enforcement. Linkages across the data sources for broader analytical purposes would require approval from each of the three agencies, and the full database has not been widely used for analysis.
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From page 88... ...
Such an approach would combine a behavioral model of the decision to migrate, analyzed using survey data, with a model of the stochastic process governing apprehensions, analyzed using administrative data. Although this approach can produce estimates of the flow of unauthorized migrants across the border, it incorporates assumptions about migrant behavior and the statistical properties of apprehensions that may not be open to empirical validation.
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From page 89... ...
Even though the smugglers of illegal aliens already appear to have relatively accurate information on the rates of apprehension and successful entry into the United States, important operational information could nevertheless be safeguarded through broad geographic identifiers that link, for example, to USBP sectors rather than individual USBP stations. Others have argued that releasing administrative data risks violating the privacy of individuals who are apprehended.
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From page 90... ...
• ecommendation 5.1: DHS should integrate apprehensions data R from USBP, OFO, and ICE for analytical purposes. • onclusion 5.1: Administrative data from DHS are alone insuf C ficient to estimate the flow of unauthorized migrants across the U.S.–Mexico border.
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From page 91... ...
ADMINISTRATIVE DATA ON UNDOCUMENTED MIGRATION 91 publicly available for research use, as that would allow DHS to engage with the broader scientific community to develop, apply, and continually refine specific modeling approaches. DHS could develop ways of constructing masked and/or aggregate files for public release in order to protect sensitive information.
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