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.