Re: Main and interaction effect in Cox Prop Hazards

Posted by Bruce Weaver on Sep 22, 2019; 1:05pm
URL: http://spssx-discussion.165.s1.nabble.com/Re-Main-and-interaction-effect-in-Cox-Prop-Hazards-tp5738390p5738398.html

Fair points, Rich.  It would be helpful if the OP posted the syntax.  

Also, if I'm using a command that allows factor variables, if it also has
EMMEANS, I like to generate the fitted values (and pairwise contrasts)
corresponding to the interaction term to make sure I've got things right.


Rich Ulrich wrote

> Bruce,
> I hate it when interactions have to be interpreted, especially if it
> is possible that the program generated them and I don't have control.
> Also, telling a program that this is a "factor" and not a continuous
> "variable" raises the problem that, for 0/1,  if the program takes "1" as
> the reference group, it reverses the sign of the B obtained. PITA.
>
> Further:  if two variables are coded as 0/1  and the interaction is their
> simple product - instead of the "centered" product - then the
> interaction's
> B is correlated with the main-effects' B's, and affects their magnitude in
> the equation that has them all.
>
> I recognize that this OP needs basic help with interpretation of the
> model,
> which you provided.  I was skipping that, because the main thing relevant
> to the question is that there /is/  no interaction effect worth worrying
> about, according the Wald test.
>
> --
> Rich Ulrich

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