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# Re: Subject: Re: st: Odds ratio

 From Marcello Pagano 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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