I think it goes the other way. The criminal has to ask if what they might take from you is worth their life. If they are going to rob you and they think you might have a gun they will wait until they know you will not be home. Which is fine for me. Take my stuff, im insured, but you threaten my family.... that is another story.
More stats on the effect of allowing concealed weapon permits and violent crime.
http://www.gunsandcrime.org/florccw.html