Mass shootings such as that carried out Wednesday night in Charleston, S.C., not only seem to have become more commonplace: Research on injury prevention shows that they have become more frequent, and more deadly, over the last three decades.
Defining mass shootings as outbreaks of firearms violence in which four or more victims were killed and the shooter was unknown to most of his victims, researchers from Harvard's School of Public Health and Northeastern University, found that, in the roughly two-year period that ended in September 2013, a mass shooting occurred on average every 64 days.
In the preceding 29 years, such shootings occurred on average every 200 days.