The Harvard Youth Violence Prevention Center has partnered with the city of Boston, Massachusetts to create a data system to track youth violence. The system provides continuing information about fighting, bullying, dating violence and gun carrying. Data from it show that many Boston adolescents are afraid on public transportation (as compared to home, school or street) and that most students widely overestimate the number of their classmates carrying guns. The system also provides data on neighbourhood variables such as collective efficacy. The system has been a success due to the mutual respect shown between the academic and city partners, and the mutual benefits it provides to both.