With-gun defense polls

Peter Boucher writes:

Just in case anyone's interested.

Copied from Kleck/Gertz, here are the polls from table 1
(minus those with no estimate of annual DGUs):

Survey, Where, What year, What kinds of guns, # DGUs

Field, California, 1976, just handguns, 3.1M
Bordua, Illinois, 1977, all guns, 1.4M
DMIa, U.S., 1978, all guns, 2.1M
DMIb, U.S., 1978, all guns, 1.1M
Hart, U.S., 1981, just handguns, 1.8M
Ohio, Ohio, 1982, just handguns, 0.8M
Mauser, U.S., 1990, all guns, 1.5M
Gallup, U.S., 1991, all guns, 0.8M
Gallup, U.S., 1993, all guns, 1.6M
L.A.Times, U.S., 1994, all guns, 3.6M
Tarrance, U.S., 1994, all guns, 0.8M

I've just spent a couple of hours figuring out how Kleck computed
these estimates. Kleck acknowledges that all these polls have
deficiencies when used to attempt to estimate DGUs, so he applies
various correction factors for these deficiencies to construct these
estimates. For example, the Ohio poll used a recall period of "ever",
only asked about handguns, and only asked respondents in handgun
households. So Kleck took the 6.5% who said they had used a gun,
multiplied it by the adult population of the US (190M), then
multiplied by 0.215 to correct for the question only being asked of
handgun households (I guess that he is estimationg that 21.5% of US
households have handguns), then multipled by 1.21 to correct for only
handgun uses being counted (1.21 is the ratio between all gun crimes
and gun crimes - Kleck seems to be assuming that the ratio will be
similar for DGUs) and finally multiplied by 0.237 to adjust the number
from "ever used" to "used in past year" (I don't know where this
number comes from - it seems way too high) to get an estimate of 0.8M.

These correction factors are rather arbitrary and different choices can
give wildly different results. For example, in "Point Blank", because
excluding defences against animals caused the percentage who used a
gun to drop from 12% to 7% in the DMIb poll, Kleck used a correction
factor of 7/12 to correct polls that did not exclude uses against
animals. In the Kleck/Gertz paper, this factor is not corrected for.
Another example: Since the average gun owner has had their guns for an
average of 20 years, a reasonable way to convert from a poll that
asked if the respondent had "ever used" to get uses per year, would be
to apply a correction factor of 1/20, rather than Kleck's 0.237. Just
make a different choice on these two factors causes the estimates
derived from some polls to come out in agreement with the NCVS, rather
than Kleck. For example, the estimate you get from the Bordua poll is
about 150k -- much closer to the NCVS than Kleck.

So, it cannot be said that all these polls support Kleck rather tan
the NCVS.

There is another very interesting thing about the numbers in Table 1
--- we can use them to test my hypothesis that a large number of the
gun uses are fabrications.

Some polls asked about handgun uses while others asked about all gun
uses. Now, since it is just as easy to make up a handgun use as any
sort of gun use, I would expect the percentage who used to be about the
same, no matter whether the question was asked about handguns or any
sort of gun. On the other hand, Kleck would expect the all guns polls
to give higher usage percentages by a factor of roughly 1.21. (Recall
that's the correction factor he uses for handgun-only polls).

So, I looked through table 1 and compared all the pairs of polls that
differed only in the handgun/any gun-use question. (That is, polls
that used the same recall period and so on.) For each pair I
calculated the ratio (all-gun poll)/(handgun poll). I expect this
ratio to be about 1, Kleck expects it to be 1.21.

The results:

Poll pair       Ratio
Field-Bordua    5/8.6  = 0.6
Hart-Mauser     3.79/4 = 0.9
Hart-Tarrance   2/4    = 0.5
Hart-Kleck      3.898/4= 1.0
Ohio-Gallup91   8/6.5  = 1.2
Field-LA Times  8/8.6  = 0.9
        Mean ratio = 0.9

Of the six pairs, five come out closer to my 1.0 and one closer to
Kleck's 1.21.

Hence we can see that the polls in Kleck's table 1 show evidence that
the respondents have fabricated many of the DGUs reported.

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