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Re: st: Odds ratio


From   Richard Williams <Richard.A.Williams.5@ND.edu>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>, "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   Re: st: Odds ratio
Date   Fri, 09 Apr 2010 15:15:35 -0400

At 01:38 PM 4/9/2010, Marcello Pagano wrote:
Bookmakers have no problem interpreting odds.
Why people go through all sorts of contortions to avoid odds when they
are as natural as probabilities is beyond me.
If you take m/n as your probability then m/(n-m) are your odds.  One is
easier than the other?  Very odd.
Odds aren't bad, but odds ratios are much harder.  If you tell me the 
odds are 4, I know that is the same as an 80% chance of 
success.  But, if you tell me the odds ratio is 4, that is much 
vaguer because there are an infinite number of ways to get such a 
ratio.  It could be that the odds for the two things being compared 
are 4:1, 8:2, 20:5, .4:.1, etc. etc. etc.  Unless I know what the 
odds are for one of the things being compared is, it is hard for me 
to have much perspective on what the odds ratio really means in practice.
And while I don't think odds are a hard concept, I personally still 
tend to convert them into probabilities.

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Richard Williams, Notre Dame Dept of Sociology
OFFICE: (574)631-6668, (574)631-6463
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EMAIL:  Richard.A.Williams.5@ND.Edu
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