Headtripper25:
Glad you asked.
Professors Lott and Mustard from the Chigaco University school of Law and Economics did a study in 1996 comparing the "before and after" effects, county by county, of every state that switched to allowing "carry concealed weapons" with a permit (background check and usually some training) from previously having a ban on carry.
The study is online in Adobe Acrobat version as one file:
http://teapot.usask.ca/cdn-firearms/Lott/lott.pdf (you need the free Acrobat reader available at
www.adobe.com if you want this version)
It's also available as HTML in three parts:
http://teapot.usask.ca/cdn-firearms/Lott/guncont.html
http://teapot.usask.ca/cdn-firearms/Lott/guncont_fn.html
http://teapot.usask.ca/cdn-firearms/Lott/table13.html
The opening paragraph tells the story, the rest is the proof:
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Abstract
Using cross-sectional time-series data for U.S. counties from 1977 to 1992, we find that allowing citizens to carry concealed weapons deters violent crimes and it appears to produce no increase in accidental deaths. If those states which did not have right-to-carry concealed gun provisions had adopted them in 1992, approximately 1,570 murders; 4,177 rapes; and over 60,000 aggravate assaults would have been avoided yearly. On the other hand, consistent with the notion of criminals responding to incentives, we find criminals substituting into property crimes involving stealth and where the probabilities of contact between the criminal and the victim are minimal. The largest population counties where the deterrence effect on violent crimes is greatest are where the substitution effect into property crimes is highest. Concealed handguns also have their greatest deterrent effect in the highest crime counties. Higher arrest and conviction rates consistently and dramatically reduce the crime rate. Consistent with other recent work (Lott, 1992b), the results imply that increasing the arrest rate, independent of the probability of eventual conviction, imposes a significant penalty on criminals. The estimated annual gain from allowing concealed handguns is at least $6.214 billion.
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Note the "Concealed handguns also have their greatest deterrent effect in the highest crime counties" sentence. It makes sense, because legal carry mainly affects "stranger violent crime", such as muggings, street rapes, etc...which you see less of in the more peaceful areas. CCW permits have little effect on in-home "unplanned crimes of domestic violence" one way or another.
CCW also doesn't affect "crook on crook crime" which is the most common overall type of murder.
Lott was involved in a follow-up work, where they studied the effect of legal gun carry on "mass public shootings" of every type, not just school-specific. The school events are actually the least common type of public mass killings.
That paper, titled "Multiple Victim Public Shootings, Bombings, and Right-to-Carry Concealed Handgun Laws: Contrasting Private and Public Law Enforcement" is available at:
http://papers.ssrn.com/sol3/papers.cfm?abstract_id=161637
Opening paragraph:
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Abstract:
Few events obtain the same instant worldwide news coverage as multiple victim public shootings. These crimes allow us to study the alternative methods used to kill a large number of people (e.g., shootings versus bombings), marginal deterrence and the severity of the crime, substitutability of penalties, private versus public methods of deterrence and incapacitation, and whether attacks produce "copycats." Yet, economists have not studied this phenomenon. Our results are surprising and dramatic. While arrest or conviction rates and the death penalty reduce "normal" murder rates, our results find that the only policy factor to influence multiple victim public shootings is the passage of concealed handgun laws. We explain why public shootings are more sensitive than other violent crimes to concealed handguns, why the laws reduce both the number of shootings as well as their severity, and why other penalties like executions have differential deterrent effects depending upon the type of murder.
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Note the phrase "our results find that the only policy factor to influence multiple victim public shootings is the passage of concealed handgun laws" - that sounds radical until you stop and think. See, virtually all of these events end in the suicide (or attempted suicide) of the killer. "Deterrence after the fact" simply isn't an issue, you can't threaten somebody with jail when they plan on blowing their brains out.
What you CAN do is "deny them glory", by blowing their butts to hell the moment they pop up and act out. "Loony killed by enraged grandma" doesn't have the "glory factor" to a nutcase the way "embittered victim lashes out at society, society takes it on the chin" does, which is how these losers see it and how they WANT to see it.
Follow?