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Date:         Thu, 1 Sep 2005 09:59:33 -0300
Reply-To:     Hector Maletta <hmaletta@fibertel.com.ar>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         Hector Maletta <hmaletta@fibertel.com.ar>
Subject:      Re: Decomposing interaction term in Cox Regression
Comments: To: "David M. Fresco" <fresco@kent.edu>
In-Reply-To:  <D5D0B9C4-BAC6-4274-88E1-E7B4B294A4AA@kent.edu>
Content-Type: text/plain; charset="us-ascii"

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.

Hector

> -----Original Message----- > From: David M. Fresco [mailto:fresco@kent.edu] > 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. fresco@kent.edu > Department of Psychology Voice: (330) 672-4049 > Kent State University Fax: (330) 672-3786 > 226 Kent Hall Annex > P.O. Box 5190 http://dept.kent.edu/ > psychology/ > Kent, OH 44242-0001 http://www.personal.kent.edu/ > ~dfresco/ > > ListOwner of Helplessness http://psych.upenn.edu/~fresco/ > helplessness.html Listowner of Mindfulness > http://listserv.kent.edu/archives/ > mindfulness.html > > > > __________ Informacisn de NOD32 1.1207 (20050831) __________ > > Este mensaje ha sido analizado con NOD32 Antivirus System > http://www.nod32.com > >


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