From: oleary@cbnewsh.cb.att.com (brian.m.leary)
Subject: Re: Kennesaw, 1986: Burglary Still Down 85%
Organization: AT&T
Date: Sat, 23 Jan 1993 05:01:26 GMT
Summary: population increase started in 1980 not 1976
	 Graphic selected tends to minimize decrease

In article <LAMBERT.93Jan21005019@nankeen.spectrum.cs.unsw.oz.au>, lambert@spectrum.cs.unsw.oz.au (Tim Lambert) writes:
> >>>>> On Tue, 12 Jan 1993 16:15:56 GMT, oleary@cbnewsh.cb.att.com (brian.m.leary) said:
> 
> > (Tim Lambert) writes:
> >> (brian.m.leary) said:
> >> 
> >> > The residential burglary rate in Kennesaw, Georgia dropped sharply
> >> > after a city ordinance requiring heads of household to keep at least one
> >> > firearm in their homes was passed.  The law passed early in 1982.
> >> > In 1986 the rate was still down 85% compared to 1981. (1)
> >> 
> >> This statistic is essentially meaningless.  If the crime rate
> >> fluctuates, then by picking the right two years to compare, you can
> >> get any result you want.  
> 
> > I agree with Mr. Lambert, by picking the right years you can
> > alter the results.  However I don't think this comparison is meaningless.
> >  
> > If you check Mr. Lambert's Kennesaw
> > data, you will see that 1986 had the most burglarie of any year.
> 
> > If you check Mr. Lamberts population adjusted data, you will see 86
> > is the post law peak.
> 
> > So if Kleck is calculating the decline the way Mr. Lambert thinks
> > he is, Kleck has chosen a high year for comparison and thus strengthens his 
> > case for burglary declining sharply after the Kennesaw law.
> 
> I'm having a hard time understanding this argument.  If the comparison
> shows that burglaries went up, how does this support a case that
> burglaries declined?
> 
Your numbers show 81 and 86 have the same burglary rates. 
1986 was the high post law burglary year in both your data and Klecks
data, so if Kleck calculated as you think he did he calculated using
the worse possible year for proving his case.  More on why his numbers 
differ from yours below.

> > However, Kleck and Lambert do not calculate the same way
> > since Mr. Lambert's graph shows total burglaries up or equal 
> > (I can't tell since the graph was messed up) when 81 is 
> > compared to 86 (see below).
> 
> >> Here are the burglary rates
> >> 76-86, assuming a population growth of 70%, normalized to the 76
> >> population value.  Each * represents 5 burglaries.
> >> 
> >> 
> >> **             **             **
> >> **       ** *  ** *  *        **
> >> ** ** ** ** ** ** ** ** ** ** **
> >> ** ** ** ** ** ** ** ** ** ** **
> >> 76 77 78 79 80 81 82 83 84 85 86
> >>                   ^
> >>                   Law        
> >> The rate does not appear to be lower after the law.

Notice that this graphic minimizes the visual impact of the post law 
decrease by presenting the data in two columns.

The height of the 82 column is 75 percent of the 81 height
but the 82 rate is 63 percent of 81's. Compare with the visual below:

*
*
*
* * 
* *
* *
* *
* *
8182

> >> Average 76-81 is 29
> >> Average 82-86 is 26
> >> The average after is a little lower.  To test the significance of
> >> this, I use Student's t-test.  I compute t=-0.13 with 9 df, p=0.51,
> >> that is, 51% of the time chance will produce a change this large.
> >> This obviously not significant.
> 
> > When Kleck does his calculation using total burglaries (1) he
> > gets a decline of 56% between 1981 and 1986 so obviously Mr.
> > Lambert and Dr. Kleck don't do their computations the same
> > way.  Who should I believe?
> 
> Neither of us.  You should check the calculations for yourself.
> 
> Here are my calculations:
> 1981 burglaries: 54  (data from Sociology and Social Research v74p51)
> 1986 burglaries: 70  (data originally from FBI Uniform Crime Reports)
> 
> 70/54 = 1.30 -- that's a 30% increase in number of burglaries.
> 
Do these two sources count burglaries the same way?

> You stated that the population increased 70% between 76 and 86.  If
> this trend was linear, in 81 the population was 1.35 times its 76
> value, and in 86 1.7 times.
> 
> (70/1.7)/(54/1.35) = 1.03 -- that's a 3% increase in burglaries per
>                              100k population
> 
> Now it's your turn.  Please post details of the calculations Kleck
> uses to get a 56% decrease in burglaries.
> 

Well since the population increase didn't start until 80 (1)
you might start by recalculating the burglary rates using 10
percent per year growth starting in 81.

Brian Leary

(1) Kleck, Point Blank, Page 136

Newsgroups: talk.politics.guns