The database has recorded 81 cases from 1982 all the way to the recent shootings at an Orlando gay club on June 12. According to the data, there have been a total of 670 people killed and another 647 injured in those attacks. Mother Jones, for this dataset, first defined a mass shootings as any shooting from 1982 to 2012 with four or more fatalaties. A data change in 2013 means that those more recent cases are shootings with three or more fatalaties.
It also excludes shootings that are related to more conventional crimes such as armed robbery or gang violence.
Mass shootings in the US, 1982 - 2016 (June 12)
Mouseover or click each dot for more details. Data from 1982 to 2012 include mass shootings with four or more fatalities. Following a change in the baseline in 2013 by the authorities, data from 2013 onward include mass shootings with three or more fatalities. Shootings stemming from more conventional crimes such as armed robbery or gang violence are excluded.
Source: Mother Jones