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• Quasi-experimental statistical methods can be employed to assess the effects or effectiveness of border-enforcement measures, if the limitations of these methods are taken into account
• Different surveillance technologies likely have different effects on outcomes at the border
• There is strong evidence that deploying integrated fixed towers is associated with decreased apprehension levels, indicating deterrence of border crossings through surveilled zones
• There is weaker evidence that deploying some other surveillance technology might be associated with elevated apprehension levels, indicating augmentation of the Border Patrol's situational awareness of border crossings

Homeland Security Operational Analysis Center researchers sought to establish a causal connection between border-enforcement actions or policies and metrics that might be used to measure relevant outcomes at the border. Applying quasi-experimental methods, they investigated the impact of surveillance technology on levels of U.S. Border Patrol apprehensions of unlawful border-crossers between ports of entry along the southwest border. Their analysis offers insights into some of the effects of surveillance technology and serves as a demonstration of concept for the usefulness of such statistical methods. The most robust finding is that deploying integrated fixed towers (IFTs) is associated with decreased apprehension levels in the zones of deployment. Although the researchers emphasize ambiguity in the meaning of the results and the uncertainty in statistical inference with relatively small numbers of deployments, they concluded that there is strong evidence that some migrants were deterred from crossing surveilled areas of the border. The results are more inconclusive for the other surveillance assets—but there are suggestions that, unlike IFTs, tactical aerostat systems (TASs) (and, to a lesser extent, other technologies) elevate apprehension levels, which points to a boost to the U.S. Border Patrol's situational awareness. Statistical methods hold both promise and limitations for the study of the impact of border-enforcement measures beyond the analysis in this study. Although these methods cannot, on their own, yield clear answers in every case, they do have the potential to help operational commanders and policymakers understand and anticipate the impact and effectiveness of different border-enforcement measures.

• Chapter One

  Introduction: Studying the Effects of Border-Enforcement Measures

• Chapter Two

  Methodology: Identifying the Effects of Surveillance Technology, Using Statistical Methods for Causal Inference

• Chapter Three

  What Do Data and Statistical Analysis Tell Us?

• Chapter Four

  The Path Forward and Conclusions: Implications for the Department of Homeland Security

• Appendix A

  Technical Details