In the five months after the passage of the mandatory gun ownership
law in Kennesaw, Georgia the residential burglary rate was down
89% from the same period the year before. Does this prove the
law worked? No – proof is difficult in these matters.
However, is it clear that the law had no effect? Hardly.
The source for this claim appears to be Kleck’s paper in “Social
Problems” v35p15, where he states there were five reported residential
burglaries in the seven months after the law, while there were 45 in
the corresponding seven months of the preceding year.
As you have noted, this isn’t enough data to conclude if the law did
or did not have an effect. Sure, there is a big reduction, but how do
we know that before year was not unusually high?
If the sequence is
7 43 4 5 6 45 5
we certainly wouldn’t conclude that the law caused the reduction.
However, there is a MUCH more serious problem with this 89% reduction
claim. From the “Criminology” v29p541 paper by McDowall et al (which
provides monthly totals) I computed the total number of burglaries in
the seven months after the law (23) and for the seven corresponding
months of the previous year (37). Something is wrong here. It’s
possible that 5 out of 23 burglaries after the law were residential
but it sure as hell ain’t possible for 45 out of 37 burglaries before
to be residential. One dataset must be wrong.
McDowall et al’s data come from the FBI’s Uniform Crime Reports.
Kleck’s data comes from a telephone conversation somebody else had
with the Kennesaw police chief.
I think the UCR data is likely to more accurate.