Date: Thu, 1 Sep 2005 09:59:33 -0300
Reply-To: Hector Maletta <email@example.com>
Sender: "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From: Hector Maletta <firstname.lastname@example.org>
Subject: Re: Decomposing interaction term in Cox Regression
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Just do the same. Plot the hazard curve for various combinations of levels
of A an B (high-high, high-low, low-high, low-low, for instance). You can do
this in various way. One is generating (with COMPUTE) the value of the
function for each subject at various given levels of A and B, plus actual
values of the other covariates, then plot the results.
> -----Original Message-----
> From: David M. Fresco [mailto:email@example.com]
> Sent: Thursday, September 01, 2005 9:53 AM
> To: Hector Maletta
> Subject: Re: Decomposing interaction term in Cox Regression
> On 01 Sep 2005, at 8:47, Hector Maletta wrote:
> > David,
> > I don't understand what your difficulty is, since you say
> you have a
> > good grasp of interactions in regression. The idea is basically the
> > same. In this case, you have found that the hazard rate for relapse
> > increases with A (at constant B), with B (and constant A) and
> > furthermore these two factors reinforce or potentiate each other as
> > indicated by the significant interaction of both. This increase in
> > hazard for subjects with higher AB product, of course, is
> supposed to
> > be proportional along time, i.e. to affect all patients at
> all times.
> > Suppose A=sex and B=smoker, you found that one sex has more
> risk than
> > the other, smoking also increases the risk, and furthermore, the
> > effect of smoking is dependent on sex and vice versa.
> > Hector
> Thanks for the reply. I should have added that A and B are
> both continuous measures. The way I handle such interaction
> terms in OLS is to solve the full model at various levels of
> the predictors in a manner described in Cohen and Cohen.
> Although I understand OLS pretty well, I am a bit out of my
> element in interpretting and reporting the hazard values that
> would emerge from some decomposition of my interaction term.
> Any further suggestions?
> David M. Fresco, Ph.D. firstname.lastname@example.org
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