Re: odds ratio to chi square conversion

Posted by Bruce Weaver on Jul 16, 2012; 7:18pm
URL: http://spssx-discussion.165.s1.nabble.com/odds-ratio-to-chi-square-conversion-tp5713894p5714260.html

Ryan is correct.  From the article (http://www.aliquote.org/pub/odds_meta.pdf):

"The standard logistic distribution [7] has variance pi^2/3, so a difference in ln(odds) can be converted to an approximate difference in NED [i.e., Normal equivalent deviate] by dividing by pi / SQRT(3), which is 1.81 to 2 decimal places."

I suspect that the R function I mentioned in the other thread uses this method.  

R B wrote

*Correction:

sd = pi / sqrt(3) ~ 1.81

Ryan

On Jun 30, 2012, at 4:38 PM, R B <[hidden email]> wrote:

> Rich,
>  
> I haven't read the article, but my guess is that they suggested dividing by 1.81 since that value approximates the standard deviation of the standard logistic distribution, which is pi/3.
>  
> Ryan
>  
> On Sat, Jun 30, 2012 at 3:46 PM, Rich Ulrich <[hidden email]> wrote:
>
> That's an interesting note.  I'm not sure why it makes
> good sense, to divide the ln(OR) by 1.81.  But the
> writer does make good sense in suggesting that a
> good measure of effect size is log(OR), and what you
> need for further information is not the N, but the
> standard error. (I think he is suggesting that.)
>
> The original question was about converting an OR
> to a chi-squared test, in the context of meta-analysis.
> I doubt why anyone should want to do that, except
> as an intermediate step to finding the error term --
> the chi-squared statistic itself is a *test* statistic, and
> is poorly suited for "effect size".  Where it is appropriate,
> the OR is a fine measure of effect, and log(OR) is the
> version that serves as an interval-scaled measure.
>
> --
> Rich Ulrich
>
>
> Date: Sat, 30 Jun 2012 07:44:43 -0700
> From: [hidden email]
> Subject: Re: odds ratio to chi square conversion
> To: [hidden email]
>
> FYI:
>
> http://www.ncbi.nlm.nih.gov/pubmed/11113947 
>  
> ~~~~~~~~~~~
> Scott R Millis, PhD, ABPP, CStat, PStat®
> ...
>