Date:         Mon, 14 Jun 2010 10:57:16 -0400
Reply-To:     Ryan Black <ryan.andrew.black@GMAIL.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Ryan Black <ryan.andrew.black@GMAIL.COM>
Subject:      Re: when to do separate analysis for gender
In-Reply-To:  <279E0CB25CBDEF4DB4A50E89328780E2019F7CEC@CHEXCMS08.one.ads.che.org>
Content-Type: text/plain; charset=ISO-8859-1

Kevin,

Could you provide a reference for retaining interaction terms that have
p-values =<.25?

Thanks!

Ryan

On Mon, Jun 14, 2010 at 10:49 AM, Viel, Kevin <kviel@sjha.org> wrote:

>  > -----Original Message-----
> > From: SAS(r) Discussion [mailto:SAS-L@LISTSERV.UGA.EDU] On Behalf Of
> Myung
> > Ki
> > Sent: Monday, June 14, 2010 8:42 AM
> > To: SAS-L@LISTSERV.UGA.EDU
> > Subject: when to do separate analysis for gender
> >
> > Hello everybody,
> >
> > I have a question on when we need to do separate analysis and when to do
> > combined analysis.
> > To decide this, we have done descriptive analysis by gender and test many
> > interaction by gender term as well.
> > But the results were not straightforward for that decision.
> >
> > I prefer to do separate analysis complemented by gender interaction. This
> > is
> > because although combined analysis is able to present estimates for sex
> > variable, which separate analysis cannot, it doesn't allow comparison
> > between gender with values. But others in my group think differently.
> >
> > So I would like to your opinion and possibly a reference on this issue,
> > Any comments will be appreciated.
>
> Myung,
>
>  We need much more information.  For instance, your model and a brief
> description of study design.  The "interaction" might not sufficiently be
> handled by inclusion of the term "sex*exposure".  How you code the terms
> could be a problem.
>
>  I think separate analyses are justifiable as the more conservative
> approach.  Remember, that you can model a circle with a triangle, but the
> fit might not be the best.  Sex as a dichotomous variable, to me, is always
> questionable, but how objectionably so depends on the study question.
>
>  Note that I used the term sex and you used gender.  I made an assumption.
>  I prefer gender as a behavioural construct and sex as a physical one.
>  Despite being classically treatment as a dichotomous trait, sex is not male
> or female on a refined level.  For instance, X0 (Turner's syndrome) and XXY
> (Klinefelter's syndrome) occur more frequently than some might expect.
>  Also, the levels of "sex" hormones do not always accurately classify
> physical or karyotypic sex.  However, as measurements of sex hormones or
> other traits are rarely done, we are usually stuck with female and male sex.
>
>  By the way, I have seen recommendations that p-values, if you will, on
> interaction terms as high as 0.25 should mean that the term should be
> retained in the absence of a (strong) a priori argument.
>
> -Kevin
>
>
>
> Kevin Viel, PhD
> Senior Research Statistician
> Patient Safety & Quality
> International College of Robotic Surgery
> Saint Joseph's Translational Research Institute
>
> Saint Joseph's Hospital
> 5671 Peachtree Dunwoody Road, NE, Suite 330
> Atlanta, GA  30342
>
> (678) 843-6076:   Direct Phone
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> kviel@sjha.org
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