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Re: Subject: Re: st: Odds ratio


From   Marcello Pagano <pagano@hsph.harvard.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: Subject: Re: st: Odds ratio
Date   Sat, 10 Apr 2010 12:59:27 -0400

True, except your transformation is linear--and since we usually round off to the closest degree, that makes Fahrenheit approximately twice as precise as Centigrade :-) --whereas the transform from odds to probabilities is not. The transformation is one-to-one and onto so the information on the two scales is
the same, but the feel is slightly different.

This all changes when you take the ratios. The biggest difference with the ratios, of course, is that the prior odds ratios are the posterior odds ratios, making case-control studies sound, something that cannot be said of relative risks. (The relative odds of having lung cancer for smokers to non-smokers is the same as the relative odds of being a smoker for those with lung cancer to those without lung cancer, for example.) Thus it is much more than a matter of taste as in the Fahrenheit versus Centigrade comparison; or pounds
versus Kilos, or miles versus ......

m.p.



Clyde Schechter wrote:
Although not precisely analogous, I think of the odds ratio vs. risk ratio
issue as being a bit like temperature measurements in different units. It's mostly a matter of what you're accustomed to. Just as it is easy to
convert between odds and probabilities, it is also easy to convert
temperatures between Farenheit and Celsius.  Yet, having grown up in the
US, I have had, as far back as I can remember, an instinctive
understanding of what a given Farenheit temperature feels like and its
implications for getting dressed.  But only after extensive travels to
Europe was I finally able to intuitively understand temperatures reported
in Celsius.  And notwithstanding a physical chemistry course in college, I
still have no intuitions about temperatures reported in Kelvins.


Clyde Schechter, MA MD
Associate Professor of Family & Social Medicine
Albert Einstein College of Medicine, Bronx, NY, USA



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