And it wasn't just casualties. Mother Jones found that 24 of the last 62 worst mass shootings have taken place in the past seven years alone. That seemed like a clear increase.
Why the difference? Fox is looking at all mass shootings involving four or more victims — that's the standard FBI definition. Mother Jones, by contrast, had a much more restrictive definition, excluding things like armed robbery or gang violence. They were trying to focus on spree killings that were similar in style to Virginia Tech or Aurora or Newtown. The definitions make a big difference: On Fox's criteria, there's no uptick. On Mother Jones', there's a clear increase.
Meanwhile, by either criteria, there does seem to be a surge in mass shootings in 2012. But it's unclear whether that's a one-year blip or not.
So, duly noted. One final point, though: Even if mass shootings are simply staying constant, and not actually increasing, that might still be of interest given that the overall rate of gun violence and homicide in the United States appears to be on the downswing.