From: oleary@cbnewsh.cb.att.com (brian.m.leary)
Subject: Kennesaw, Georgia: residential burglary down 89%
Organization: AT&T
Date: Thu, 31 Dec 1992 21:03:14 GMT
Keywords: Mandatory Gun Ownership 

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.

Tim Lambert:

>TL>Kennesaw Burglaries 1976-1986
>TL>76 77 78 79 80 81 82 83 48 85 86
>TL>41 21 22 35 35 54 35 35 29 32 70

and Tim Lambert:

] The raw data is presented as graphs showing burglaries in Morton Grove
] and Kennesaw for the period 1976-86.  The burglary rate in Kennesaw
] appears stable, while the burglary rate in Morton Grove is noticeably
] lower.  The paper's authors did an interrupted time series analysis on
] the data:  the change associated with the Kennesaw ordinance was an
] insignificant increase of 0.2 burglaries/month, the
] change associated with the Morton Grove ordinance was a
] statistically significant decrease of 4.5 burglaries/month,

] Clearly the Kennesaw ordinance had no effect.  It seems unlikely that
] the Morton Grove ordinance caused the reduction (unless there a
] significant number of burglars who burgle primarily to get guns).  The
] authors also considered the effect of the Evanston gun ban on
] burglaries and found a not quite significant (p=.13) decrease.

] The data does not support the theory that gun ownership deters
] burglaries.

By

Overlooking the fact that the population of Kennesaw grew about
70% during this period.

And overlooking the fact that the author used total burglaries
and not residential burglaries.  (The burglars might stay in town
but change their targets to the unoccupied businesses.)

And maybe by

setting the study length just so the author could get the desired
result.  Why such a long time series?  A symbolic law like
this might have only a short term effect.  What is wrong with
one year less on each end?  (Because it would "prove" the law
decreased crime?)

Peter Boucher(?):

> Let's look at a graph of the data:

> burglary
> rate
>                          |          /--
>   70 |                   |          |XX
>      |                   |          |XX
>   60 |               /--\|          |XX
>      |               |XX |          |XX
>   50 |               |XX |          |XX
>      | --\           |XX |          |XX
>   40 | XX|     /----/ XX |----\     |XX
>      | XX|     |XX XX XX |X XX ----/ XX
>   30 | XX|     |XX XX XX |X XX XX XX XX
>      | XX\----/ XX XX XX |X XX XX XX XX
>   20 | XX XX XX XX XX XX |X XX XX XX XX
>      --------------------|---------------------
>        76 77 78 79 80 81 82 83 84 85 86   Year
>                          |
>                          |
>                The year the law passed.

Not clear at all that there was no effect.

And Peter Boucher(?):

> Mr. Lambert supplies no data regarding years before 76 nor after 86,
> so both those years are seen more-or-less in isolation, and thus are
> suspect, regarding their relevance.  We don't know what might have
> caused an increase in 76 or 86.  We don't know what might have caused
> a decrease in 77.  We also don't know what caused a decrease in 82,
> and cannot rule out the possibility that it was caused by the law.

And Tim Lambert:

>In an earlier posting, Peter stated that it was apparent that "the law
>had a marked effect".  In order for this to be apparent, it is
>necessary to ignore the years 76 and 86.  The paragraph above is a
>rationalisation for this.

We don't know if it is necessary to ignore 76 and 86, it might just
be necessary to include some additional years (or adjust for
population increases or use the residential burglary rate).
By the way, Mr. Lambert seems to be acknowledging that the result
of the study hinges on choosing the particular interval used -
that the conclusion would be reversed by shortening the interval
by a year on each end.  What kind of "proof" is this study anyway?

When the population adjusted residential burglary rate is calculated
for the same time period I think that you will find a large decrease
in the rate.  Something like 87% comes to mind (or maybe only 82%).

Brian Leary

PS:  I enjoyed Mr. Lamberts response to my last post, but I felt it was
somewhat non-responsive to the population and burglary-type questions
I raised.  The other methods of normalizing the data he suggested would be
interesting but I think population and burglary-type are most relevant.  
Newsgroups: talk.politics.guns