From: elm@cs.berkeley.edu (ethan miller)
Newsgroups: soc.college,talk.rape
Subject: Re: fraternities
Date: 14 Apr 92 05:18:48 GMT
Article-I.D.: terroris.ELM.92Apr14001848
	<1992Apr12.123401.4989@ac.dal.ca>
	<1992Apr12.174643.14068@midway.uchicago.edu>
	<1992Apr14.055358.20185@cis.ohio-state.edu>
Reply-To: elm@cs.berkeley.edu
Organization: utter chaos
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In-reply-to: schubach@boa.cis.ohio-state.edu's message of Tue, 14 Apr 1992 05:53:58 GMT

In article <1992Apr14.055358.20185@cis.ohio-state.edu> schubach@boa.cis.ohio-state.edu (bernard william schubach) writes:
=>>		Frat Rapes	Non-Frat Rapes		Total
=>>Reported	    34		      20		  54
=>>Unreported	   101		     385		 486
=>
=>Total              135               405                 540
=>Percent of Total   25%               75%                 
=>
=>>Percent Reported   25.2%	      4.9%		 10.0%

You're missing Ted's point, which is the final line.  If fraternity
members commit just 25% of the rapes on campus, then rapes by
fraternity brothers must be reported 5 times as often as rapes by
non-fraternity members.  Is this likely?

=>>Either fraternity members are five times more likely to rape or
=>>victims of fraternity rapes are five times more likely to report the
=>>rape.  (Or some combination in between, which doesn't hurt the conclusion
=>>that fraternity members are more likely to commit rape.) 
=>
=>Where in the world did you get this conclusion from?
=>What your argument says is,
=>"Suppose fraternity rapes are five times more likely to be reported than
=>nonfraternity  rapes. Therefore, fraternity members are five times more
=>likely to rape someone then nonfraternity members."

No.  The argument states that more rapes are reported per fraternity
member than per random student.  This can be caused by one of two
things:
1.  Fraternity members are more likely to commit rapes.
2.  Women who are raped by fraternity members are more likely to report
    them.

It may also be a combination of the two.  Now, if you want to assert
that (2) is the case, that's fine.  The numbers that Ted presented
show that, for (2) to be the case, women would have to be 5 times more
likely to report a rape by a fraternity member.  What basis is there
for this hypothesis?

Let's try another, similar, example.  Suppose red cars are more likely
to be pulled over for speeding.  From this, we can conclude one of two
things.  Either people driving red cars are more likely to speed, or
red cars are more likely to be pulled over when they do speed.  In
this case, I'd tend to mostly suspect the latter, as red cars are more
visible.  However, the first may play a minor role, since people who
like red cars might be more likely to speed.

Just as in the original example, a difference in observed events can
be caused by a bias in observation or a bias in events.  In the
fraternity case, events are rapes, and observations are reports of
rape.  If one group is reported to commit rape more often, then it
must either actually commit more rapes or just get reported more
frequently.  Given other evidence, I'd suspect that the former is
true.

ethan
--
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
ethan miller--cs grad student   | "Anybody not wearing 2000000 sunblock's
elm@cs.berkeley.edu             |  gonna have a REALLY bad day.  GET IT?"
#include <std/disclaimer.h>     |  -- Sarah Connor, _Terminator 2_