Here is an email I just got from Mayors Against Illegal Guns. Debunking myths is a hobby of mine, so I had to share:
I want to bring to your attention to an updated analysis we're releasing that shows there have been nearly two mass shootings per month in the United States between January 2009 and September 2013. The survey can be found here.
Using FBI data and media reports, our report describes the more than 90 mass shootings that have occurred in this nearly five-year period. The FBI defines a "mass shooting" as any incident where at least four people were murdered with a gun. The survey's findings reveal a different portrait of mass shootings in America than conventional wisdom and previous media coverage might suggest:
Oh, and there's this from Think Progress: NRA Tried To Stifle Study Showing Gun Retailers Support Background Checks.