Tim Lambert (deltoidblog AT gmail.com) is a computer scientist at the University of New South Wales.
About 2/3 of the crimes where guns are used for self defence are assaults, so this is the death rate that we should use.
Frank Crary said:
Why? As I said, attempted murders/murders would have a much (as in, order of magnitude) higher. Even if they are only a small fraction of violent crimes, their contribution would still be as great as that from assaults.
Let's see, if attempted murder/murder is 5% fatal, then there must be 500,000 of them to get the same contribution as I have assumed from assaults. That gives 25,000 homicides from attempted murder/murder and 25,000 from assaults. Oops. There aren't that many homicides.
All right, assume that the death rate from assaults is 0.3% and there are only 240,000 attempted murders/murders, which means that each one contributes 12,000 homicides.
For the assaults, guns are used for defence 1% of the time and are 80% effective = 100 lives saved.
A would-be murderer is going to give you less chance to use a gun (by shooting or stabbing first), and is going to be less then 80% effective in stopping the crime (since the murderer is less likely to be deterred by the threat of shooting -- if there is a fight to the death, the victim's chance of survival is going to be less than 50% since the attacker has the advantage of going first and both parties could die.). To get an upper bound, I'll assume guns are used for defence 1% of the time and are 50% effective = 60 lives saved.
That gives a total of 160 lives saved by defensive gun use.
