A simple pre/post comparison of time-series data conducted by Braga and colleagues (2001) found a statistically significant decrease in the monthly number of youth homicides in Boston, Mass., following implementation of Operation Ceasefire. There was a 63 percent reduction in the average monthly number of youth homicide victims, going from a pretest mean of 3.5 youth homicides per month to a posttest mean of 1.3 youth homicides per month. When control variables (such as Boston’s employment rate, and changes in citywide trends in violence) were added to the data analysis models to test whether other factors may have influenced or caused the reductions, the significant decrease in youth homicides associated with the Ceasefire intervention did not substantively change.
Citywide Gun Assaults
Ceasefire was associated with a 25 percent decrease in the monthly number of citywide gun assaults, and with a 44 percent decrease in the monthly number of youth gun assaults in district D–2. When control variables were added to the data analysis models, the significant reductions in gun assault incidents and youth gun assault incidents in District B–2 associated with Ceasefire did not change.
Calls for Service
The Ceasefire intervention was also associated with a 32 percent reduction in the monthly number of citywide shots-fired calls for service. When control variables were added to the data analysis models, the significant reduction in shots-fired calls for service associated with Ceasefire did not change.
New Handguns Recovered Citywide
Braga and Pierce (2005) found that the Ceasefire intervention made a large impact on the yearly percentage of traceable handguns that were new with a fast time-to-crime (which is the time between a firearm’s first sale at retail and subsequent recovery in a crime) recovered by the Boston (Mass.) Police Department. Simple pre/post comparisons showed that the percentage of traced handguns with a fast time-to-crime increased steadily between 1991 and 1996, reaching a peak of 53.8 percent of traced handguns in 1996. Then between 1997 and 1999, the percentage of traced handguns with a fast time-to-crime decreased dramatically to 15.6 percent and remained at this lower level through 2003. Counting 1997 as the first full year of gun market intervention, there was a 47 percent reduction in the percentage of new traced handguns in Boston, from an average of 40.4 percent between 1991 and 1996 to an average of 21.4 percent between 1997 and 2003.
Multivariate analysis (which controlled for other predictor variables) of new handguns recovered in Boston found that Operation Ceasefire was associated with a statistically significant reduction in the percentage of recovered handguns that had a fast time-to-crime. Ceasefire was associated with a 22.7 percent reduction in the average monthly percentage of all recovered handguns that were new and a 24.3 percent reduction in the average monthly percentage of all recovered youth handguns that were new, as well as with a 29.7 percent reduction in the average monthly percentage of illegal possession handguns that were new and a 17.4 percent reduction in the average monthly percentage of all recovered substantive crime handguns that were new (all reductions were statistically significant).