The common definition of a mass public shooting is an incident in which four or more victims are killed publicly with guns within 24 hours -- in the workplace, high schools, college campuses, malls, gyms, restaurants and other public places -- excluding shootings in connection with crimes such as robbery, drug trafficking or gang-related activity. By that definition, there have been 140 mass public shootings in the United States during the last 100 years.
Although mass public shootings may seem to be on the rise, newly compiled data show that there were 24 such incidents in the past decade. While that's still significantly higher than the average of the first eight decades of the 20th century, it does mark a significant decline (nearly 50 percent) from the 43 cases in the 1990s (see chart below
