John Briggs writes:
[Calculation of number of justifiable shootings deleted]
This would suggest 15,000 to
20,000 civilian justifiable woundings or 17,500 to 22,500 incidents in
which a civilian shot and hit an assailant.
Kleck does a similar calculation in "Point Blank" to get an estimate
of 10,000 to 20,000.
(This represents an awfully
high figure if there are only 80,000 civilian DGUs as the NCVS reports--of
course, the NCVS could be low.)
As you have noted, if we know A, the fraction of DGUs where the
defender shot at the criminal, and B, the fraction of DGUs where one
or more of the shots fired at the criminal actually hit, then we could
estimate the number of DGUs. Unfortunately, the only information
about what the value of A is comes from the NCVS and Kleck's survey
and if we are going to trust either one, we might as well just use the
direct estimate of DGUs that it produces.
Furthermore, we don't know B that well either. Kleck gives figures
of 37% for police and 18% for criminals (p173), but it might be
different for civilian DGUs. So, I'll use both NCVS and the Kleck
survey to estimate B and see if the results are reasonable.
NCVS: A=0.4, so B=(10,000 to 20,000)/(0.4*80,000)=30 to 60%
Kleck: A=0.16 to 0.24, so B=(10,000 to 20,000) /((0.16 to 0.24)*2,500,000) = 2 to 5%
The top of the NCVS range for B seems rather high, but 30% seems like
reasonable number for B. Kleck's survey gives numbers for B that are
way too low.