Reducing Violence by Transforming Neighborhoods: A Natural Experiment in Medellin, Colombia

"Neighborhood-level interventions provide an opportunity to better understand the impact that neighborhoods have on health."

This research was done in Medellín, Colombia, to access the effects of transit-oriented development and municipal investment in neighbourhood infrastructure on levels of neighbourhood violence. Twenty-five intervention neighbourhoods and 23 control neighbourhoods were accessed for conditions and violence levels before a 2003 transit project and after its completion in 2008.

This research tests contributes to "... a long line of research linking the prevalence of violence to neighborhood factors such as concentrated disadvantage, residential instability, and the absence of 'collective efficacy'." Municipal investment can include, for example, "efforts to improve public spaces and infrastructure, have police engage more with the community, clean up debris, and reduce social disorder - in the hopes that changing environments will trigger widespread and long-lasting reductions in violence." This study looks particularly at "1) declines in violence and 2) corresponding improvements in neighborhood conditions that might contribute to reductions in violence, including collective efficacy, citizens’ trust in the criminal justice system and reliance on police, and the availability of neighborhood amenities such as parks and cultural activities" in Medellín. In addition to extending an elevated train system to the impoverished Santo Domingo neighbourhood in the mountainous periphery and creating a cable-propelled transit system (gondola) known as Metrocable, the "municipal government made other improvements to neighborhoods serviced by the gondola, including additional lighting for public spaces; new pedestrian bridges and street paths; 'library parks'; buildings for schools, recreational centers, and centers to promote microenterprises; more police patrols; and a family police station next to a gondola station."

A 2003 household survey on neighbourhoods and violence was compared to a survey which was sent to 12 residents per block in a sample of 212 blocks selected from each of the city’s 16 districts. Follow-up interviews of 466 of the 599 respondents to the 2003 survey from intervention and non-intervention neighbourhoods were conducted. "The variables used in this analysis included indicators of service infrastructure (number of schools, sports sites, health centers), a classification of “socioeconomic stratification” based on official evaluations of city blocks used for property tax assessments, the proportion of residents eligible for welfare (from the Municipal Office of Planning), and average levels of antisocial behavior and collective efficacy...."

Results include the following: "Levels of homicide and perceived violence declined in both groups, but the drop was steeper in the intervention group, where the homicide rate dropped by 84% as compared with 60% in the control group.... Collective efficacy increased in the intervention group but remained stable in the control group. For example, the proportion of intervention-group respondents reporting that their neighbors would intervene to break up a fight among children increased from 65% to 81%, while the corresponding proportion in the control group was 71%-72% at both time points. Trust in the criminal justice system and reliance on the police for help also increased more dramatically in the intervention group. For example, the proportion of respondents who said they would call the police if they saw suspicious activity increased by 77% over time in the intervention group as compared with a 14% increase in the control group. The reported prevalence of parks and recreational areas did not change over time in either group, but reports of local opportunities to participate in cultural and educational activities increased in the intervention group."

Among the conclusions: "Although [the] study was not designed to investigate the mechanisms that produced the observed drops in violence, one account that is consistent with the pattern of changes we observed is that by improving public spaces and creating new institutions, the intervention provided more opportunities for neighbors to interact, develop trust, and become willing to intervene when the social order was threatened.... It also appears that relations between citizens and police improved in intervention neighborhoods, which could increase the efficacy of law enforcement in fighting violence and further deter would-be violent offenders.... "