Reducing violence by transforming neighborhoods: a natural experiment in Medellín, Colombia

Abstract

Neighborhood-level interventions provide an opportunity to better understand the impact that neighborhoods have on health. In 2004, municipal authorities in Medellín, Colombia, built a public transit system to connect isolated low-income neighborhoods to the city's urban center. Transit-oriented development was accompanied by municipal investment in neighborhood infrastructure. In this study, the authors examined the effects of this exogenous change in the built environment on violence. Neighborhood conditions and violence were assessed in intervention neighborhoods (n = 25) and comparable control neighborhoods (n = 23) before (2003) and after (2008) completion of the transit project, using a longitudinal sample of 466 residents and homicide records from the Office of the Public Prosecutor. Baseline differences between these groups were of the same magnitude as random assignment of neighborhoods would have generated, and differences that remained after propensity score matching closely resembled imbalances produced by paired randomization. Permutation tests were used to estimate differential change in the outcomes of interest in intervention neighborhoods versus control neighborhoods. The decline in the homicide rate was 66% greater in intervention neighborhoods than in control neighborhoods (rate ratio = 0.33, 95% confidence interval: 0.18, 0.61), and resident reports of violence decreased 75% more in intervention neighborhoods (odds ratio = 0.25, 95% confidence interval 0.11, 0.67). These results show that interventions in neighborhood physical infrastructure can reduce violence.

Figure 1.

Diminishing violence in 25 Metrocable intervention (I) neighborhoods and 23 matched control (C) neighborhoods, Medellín, Colombia, 2003–2008. Violence decreased in both groups of neighborhoods, but intervention-group neighborhoods enjoyed a greater decrease than their matched comparison neighborhoods. The bars plot estimated changes in the log homicide rate and the log odds of affirmative responses to the survey-based measure of perceived violence. (Since violence and homicide declined over time, the bars report negative numbers b, with 1 − exp(b) interpretable as the percent reduction in the outcome between 2003 and 2008.) Estimates of intervention effects appear to the left of the bars, along with corresponding 95% confidence intervals (CI).

Figure 2.

Improvement in community resources in 25 Metrocable intervention (I) neighborhoods (black bars) and 23 matched control (C) neighborhoods (gray bars), Medellín, Colombia, 2003–2008. Conditions improved in both groups of neighborhoods, but intervention-group neighborhoods enjoyed greater improvements than their matched comparison neighborhoods. The bars plot estimated changes in the log odds of endorsing the average scale item for each survey-based outcome. (The outcomes increased, so their bars report positive numbers b, with exp(b) − 1 interpretable as percent increase over time.) Estimates of intervention effects appear at the right of the bars, along with corresponding 95% confidence intervals (CI). Intervention neighborhoods experienced greater improvement on all measures except neighborhood amenities.