migration. In particular, the sample size requirements for traditional national household surveys would be considerable, especially if one wanted precise flow estimates by the nine geographic sectors into which USBP divides the southwest border. The ever-changing nature of migration flows would also create design challenges for geographically specific estimates. Although sample sizes can be smaller for probability surveys that focus on migrants (such as EMIF-N), changing patterns of migration would still create design and analysis challenges. Moreover, although EMIF-N shows great potential for DHS purposes, its adaptive design makes assessing its accuracy problematic.

Estimating annual flows in a timely fashion using survey data is a great challenge, and doing so on a quarterly and border sector/subregion basis is an even greater challenge. For border flow estimates to have practical value, survey data would need to be collected, analyzed, and released in a timely fashion. Most of the existing surveys do not meet these criteria, and only one—ENOE—is currently capable of providing quarterly estimates on a timely basis (although EMIF-N might also have the potential to provide such timely data). There are a number of key bits of information on migration and border crossing that ENOE does not collect (e.g., documentation status at crossing and border crossing location); questions on those items could, in principle, be added to the ENOE survey instrument. Given the dynamic nature of the migration process, however, questions about the migration process that are salient today may be less so in the near future. Thus, the questions added would have to be limited.

Such improvements could prove useful to researchers and others, and they would be welcome by the panel (as would, for example, improvements in the timeliness of EMIF-N). But from the perspective of estimating flows on an annual or quarterly basis, such modifications would still take place against the backdrop of larger limitations and complexities relating to sample size and survey design. The report also notes the administrative and implementation challenges arising from the fact that ENOE falls under the jurisdiction of the government of Mexico. These challenges would be no less salient if the U.S. government attempted to put in place a new dedicated migration survey in Mexico. Although surveys, especially those that focus specifically on migration, can provide a wealth of information about the migration process, they are not sufficient by themselves in meeting the needs of DHS for obtaining estimates of unauthorized migration flows across the U.S.–Mexico border on an annual or quarterly basis. The panel believes that, although DHS could benefit from engaging with entities in Mexico that collect survey data relevant to the analysis of unauthorized migration, it should not invest substantial resources in making changes to existing surveys or in implementing a new survey for the purpose that is the subject of this study.



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