Options for Estimating Illegal Entries at the U.S.-Mexico Border (2013) / Chapter Skim
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6 Model-Based Approaches to Estimating Migration Flows
6 Model-Based Approaches to Estimating Migration Flows
Pages 93-110
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From page 93... ...
For example, neither the emergence of drug violence along the border nor the severe economic recession in the United States were anticipated as recently as 5 years ago. The need for accurate estimates at the border at a geographically detailed level introduces additional challenges.
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From page 94... ...
These methods include conventional approaches, such as probability models, regression models, and spatiotemporal processes, and more recent methods such as agent-based modeling. To fit a model, one wants to have a training sample for which both the explanatory variables (such as economic pressure, enforcement effort, point of origin)
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From page 95... ...
. This simple thought experiment involves providing telephone cards to undocumented immigrants who are apprehended in the United States and are then returned to the Mexican side of the border.
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From page 96... ...
This issue might be addressed by having the migrant answer simple questions at the time of phone card activation based on demographic information collected at the time of apprehension. Third, it is necessary to ascertain whether the location from which the migrant activates the card is the migrant's final destination (be it in Mexico or the United States)
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From page 97... ...
Predictions from a model that are not paired with estimates of their prediction error have limited value. This chapter reviews several approaches to survey-informed modeling and, to the extent possible, offers some comparative guidance in the context of estimating unauthorized migration flows.
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From page 98... ...
In the case of undocumented migrants, homophily might occur when the initial group of seeds from family members in four Mexican states, they modified the initial geographic distribution into a Poisson regression model in which the response was the number of attempts before the first successful trip and the mean of the Poisson included covariates related to economic factors, gender, and other variables that might affect the success rate. They also (coarsely)
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From page 99... ...
There have been some applications of link-tracing sampling to unauthorized border crossings. Two such efforts have been discussed in Chapters 3 and 4: the Mexican Migration Project and the Mexican Migration Field Research Program.
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From page 100... ...
They describe a system of four submodels, each of which is tuned with historical data and which interact to produce a probabilistic model for immigration flows. The four submodels are as follows: • a multinomial logit model, as in Ben-Akiva and Lerman (1985)
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From page 101... ...
In principle, however, this type of complex probability modeling could be useful to address several aspects of illegal migration flows, with the exception of the probability of a successful first attempt. Regression Models Multiple linear regression modeling is a standard tool in demography and econometrics.
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From page 102... ...
On the negative side, much of the previous literature was developed using data from before 2005, and it is clear that the illegal immigration process has changed in important ways. Nonetheless, using historical survey data and administrative records, a multiple regression model of some kind (including multivariate regression, principal components regression, Cox proportional hazards regression, and so on)
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From page 103... ...
However, the regression modeling approach will not do a good job of tracking changing mechanisms of migration, and it is unlikely to provide fine geographic detail given the kinds of survey data currently available. Over time, as the migration process evolves and the measures of the inputs become outdated, the validity of the model will drift, and its predictive accuracy will surely decline.
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From page 104... ...
Prado and West (2010) offer a recent survey of the area, with special emphasis on dynamic time series models, which seem likely to be the type of time series model most relevant to estimating immigration flows when there may be feedback effects (e.g., if increased flow triggers increased border security)
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From page 105... ...
Such models extend time series analyses to include spatial correlation structure. Simple versions might allow association among flows in Mexican states for decisions about whether to immigrate, while more complicated versions might be able to capture discouragement at particular border-crossing locations, redirection of flow due to fences or smuggling cartels, and so on.
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From page 106... ...
. Agent-based modeling represents a new strategy for modeling immigration flows using data from surveys and official records.
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From page 107... ...
Also, agent-based models are easy to assess; if the emergent behavior is unreasonable, then the model is inadequate. In the context of modeling immigration flows with an agent-based model, administrative data and surveys offer important opportunities for model tuning and falsification.
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From page 108... ...
CONCLUSION Existing surveys and administrative data sources do not suffice to estimate some important aspects of the migration process; two fundamental data gaps include the proportion of undocumented migrants who cross the border undetected and the proportion of migrants who were successfully deterred after one or more apprehensions. The use of modeling approaches informed by survey data and administrative data is therefore necessary for estimating the flows of unauthorized migrants across the U.S.–Mexico border.
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From page 109... ...
This out-of-sample validation approach would have allowed the panel to compare the predictive ability of different models and explore the importance of the various assumptions underpinning those models. Although the panel was aware that DHS has been considering specific modeling approaches (e.g., capture-recapture methods using apprehensions data)
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