An impact evaluation found that the intervention generated a 19% decrease in reported crime in the areas under direct surveillance, relative to the sample average. Specifically, statistically significant impacts were found for violent crime (26% decrease) and property crime (17% decrease). No evidence of a spillover effect was detected. That is, crime reports did not change much in the areas close to those where the cameras were installed (in a radius of 120 to 300 meters) [1].
In addition, the number of arrests per month dropped by 11% relative to the sample average. The results suggest that this decrease in arrests is due to a deterrent effect rather than an incapacitation effect. The researchers estimated that the number of crimes deterred due to direct surveillance was 67 events per month, which over 10 months totaled 670 events (10 months is the average time during which the areas were under direct surveillance).
The study analyzed the results in 70x70-meter grids for the city of Medellín.