Cool, then the evidence should be easy to produce. I thank you in advance for providing it.
Easy, but tiresome. If you want to dig it up yourself, it's available on-line at the NACJD. Just register and type in your query. That's the only source I know that tries to track multiple-incident homicides.
Number of deaths due to mass shooting sprees / number of deaths due to shootings.
If you can provide hard numbers on the number of deaths due to mass shooting sprees --- or even a hard definition of "shooting sprees," you can probably work that ratio out for yourself.
In 2005, there were 12,352 homicides committed with firearms. In 2004, there were 11,624. In 2003, 11,900. To a first approximation, we can claim there are about 12,000 firearm homicides per year in the USA, a number I will project forward to 2008. (CDC data only goes up to 2005).
CBS News compiled a list of "shooting sprees" recently and identified five in the USA : Kirkwood, MO; Mount Vernon, WA, NIU, Omaha, and Cleveland (which was 2007, not 2008). Total number of victims was less than 30.
So the ratio you're looking for is approximately 1/400. Even if you assume that CBS's reportage is incomplete and the actual number of "sprees" is double what they reported, you're still looking at one half of one percent of all firearm-related homicides being related to a "shooting spree."
Of course, the real comparison isn't the number of firearm deaths vs. the number of shooting spree deaths, but the number of firearm deaths vs the number of non-firearm deaths (more accurately, homicides). In 2005, the number of homicides
of all types other than firearm-related was 5772. Firearms cause more than 2/3 of all homicides in 2005. The numbers are comparable for other years.
But the actual question is whether firearm-related injuries are more severe than non-firearm related injuries, and unfortunately I'm at home right now and the data are mostly behind a subscribers-only firewall, so I don't have access to it. But one piece of evidence I
could find ("Trauma," by Moore et al.) states that "assaults involving firearms are 12 times more likely to result in death than non-firearm related assaults."
So, I stand by my statement. People without guns hurt people. People with guns kill people.
Your chances of death are twelve times greater if your assailant is armed with a gun than if he isn't.
Therefore, I think it's both sensible and appropriate to take all reasonable measures to keep guns out of the assailant's hands, including removing them if necessary from non-criminals as well. (The US DOJ statistics support this as well -- they estimate about 100,000 "defensive uses of guns" per year vs. 1.2 million gun-related crimes.)