Date: Thu, 1 Sep 2005 09:47:02 0300
ReplyTo: Hector Maletta <hmaletta@fibertel.com.ar>
Sender: "SPSSX(r) Discussion" <SPSSXL@LISTSERV.UGA.EDU>
From: Hector Maletta <hmaletta@fibertel.com.ar>
Subject: Re: Decomposing interaction term in Cox Regression
InReplyTo: <F88302358936451B85AA97ACB3583E1E@kent.edu>
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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
> Original Message
> From: SPSSX(r) Discussion [mailto:SPSSXL@LISTSERV.UGA.EDU]
> On Behalf Of David M. Fresco
> Sent: Thursday, September 01, 2005 8:18 AM
> To: SPSSXL@LISTSERV.UGA.EDU
> Subject: Decomposing interaction term in Cox Regression
>
> Colleagues:
>
> I am hoping for some help in undertaking a decomposition of
> an interaction effect in Cox regression.
>
> I am tracking when relapse occurs in a sample of individuals
> as a function of what treatment they received as well as two
> additional factors A, B and A*B.
>
> The output indicates that the interaction of A*B is
> significant and a get a B and SE of B in the output. I am
> certainly familiar with solving interactions for OLS, but
> would welcome some suggestions on how to interpret this interaction.
>
> Below is essentially the syntax I used.
>
>
> COXREG relapse
> /STATUS=censored(0)
> /STRATA = txcond
> /METHOD=ENTER a /METHOD=ENTER b /method = ENTER a*b
> /CRITERIA=PIN(.05) POUT(.10) ITERATE(20) .
>
> Thanks in advance and I would appreciate my email being cc'ed
> to responses as I take the digest.
>
> 
> David M. Fresco, Ph.D. fresco@kent.edu
> Department of Psychology Voice: (330) 6724049
> Kent State University Fax: (330) 6723786
> 226 Kent Hall Annex
> P.O. Box 5190 http://dept.kent.edu/
> psychology/
> Kent, OH 442420001 http://www.personal.kent.edu/
> ~dfresco/
>
> ListOwner of Helplessness http://psych.upenn.edu/~fresco/
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