Re: Main and interaction effect in Cox Prop Hazards

Posted by jaycamh on Sep 21, 2019; 2:32pm
URL: http://spssx-discussion.165.s1.nabble.com/Re-Main-and-interaction-effect-in-Cox-Prop-Hazards-tp5738390p5738395.html

Thank you Bruce.

Sent from my iPhone

> On Sep 20, 2019, at 6:02 PM, Bruce Weaver <[hidden email]> wrote:
>
> Rich Ulrich wrote
>> I'm not sure what Bruce was saying about coefficients.
>
> I'll try again.  Here are the B values for the two variables of interest and
> their interaction:
>
> B(drink) = 0.566 = ln(HR) for drink when ses = 0 (i.e., reference category)
> B(ses) = 0.393 = ln(HR) for ses when drink = 0 (i.e., reference category)
>
> B(interaction) = -0.094
>
> Therefore:
> 0.566 -0.094 = 0.472 = ln(HR) for drink when ses = 1
> 0.393 -0.094 = 0.299 = ln(HR) for ses when drink = 1
>
> The interaction term tests the differences between 0.566 and 0.472 (for
> drink) and between 0.393 and 0.299 (for ses).  
>
> And of course, those ln(HR) values are adjusted for the other variables in
> the model.  
>
> Is this clearer?  
>
>
>
>
> -----
> --
> Bruce Weaver
> [hidden email]
> http://sites.google.com/a/lakeheadu.ca/bweaver/
>
> "When all else fails, RTFM."
>
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