Mexican drug war may have increased homicide rates

Because the Mexican military operations were directed at municipalities rather than entire states, the authors defined regions of analysis to be a municipality that received the intervention as well as its neighboring municipalities.

This study is more statistically rigorous than two previous articles about drug war death rates published in Nexos, a leading cultural and political magazine in Mexico. Those articles, authored by Fernando Escalante Gonzalbo and José Merino, were published in January and June 2011, respectively. Escalante relied on visual comparisons, while Merino used a less rigorous causal analysis to estimate the effect of the interventions.

When policymakers are faced with critical decisions, it is important they are basing their decisions on causal effects, not associations, said Espinosa. The statistical methodology used in this study will enable policymakers to compare intervened regions with other similar regions, not simply the past or national averages.

Unfortunately, many studies that claim to measure causation forget the fundamental step of explicitly showing that their units are comparable — in our case, that the regions are actually similar. Our paper emphasizes the importance of such balance checks, explained Espinosa.

Study findings suggest military interventions resulted in an average increase of nearly eleven homicides per 100,000 inhabitants across the eighteen affected regions studied. However, the estimated effects vary considerably across these regions.

“The results of our study suggest that military interventions in the Mexican drug war increased homicide rates in the short term, especially in the Juárez region,” said Espinosa. “While the effect on short-term homicide rates is only one factor Mexican policymakers must account for when deciding whether and where to send troops, measuring the effect accurately should increase their ability to find the optimal tradeoff between short-term violence and long-term objectives.”

Of the eighteen affected regions, only Rincón de Romos and Apatzingán experienced a significant reduction in the homicide rate relative to what would have been expected without the military intervention.

Conversely, the Juárez region experienced an increase in its homicide rate that is estimated to be more than twice as large as that of any other region in the study. The release notes that this finding should not be surprising. Since the 1990s, Ciudad Juárez has been notorious for displays of violence, such as more than 1,000 unsolved murders of young women between 1993 and 2003, and for being a major center of narcotics trafficking linked to the Juárez Cartel.

Removing the Juárez region, the analysis still yields a significant increase in the homicide rate. Specifically, the estimated regional average intervention effects with and without Juárez are 11.0 and 6.5, respectively.

— Read more in Valeria Espinosa and Donald B. Rubin, “Did the Military Interventions in the Mexican Drug War Increase Violence?” American Statistician 69, no. 1 (24 March 2015): 17-27 (DOI:10.1080/00031305.2014.965796)