[R] simple interactions

[Therneau, Terry M., Ph.D.]

I was right that there is an easy answer!

Thanks for the 3 quick answers, all three correct and useful.

Terry Therneau


On 04/15/2016 07:15 AM, Thierry Onkelinx wrote:
> Dear Terry,
>
> Does fitting group + age:group instead of age*group solves your problem?
>
> Best regards,
>
> ir. Thierry Onkelinx
>
>> 2016-04-15 13:58 GMT+02:00 Therneau, Terry M., Ph.D. <therneau at mayo.edu
> <mailto:therneau at mayo.edu>>:
>
>     I'd like to get interaction terms in a model to be in another form. Namely, suppose I
>     had variables age and group, the latter a factor with levels A, B, C, with  age *
>     group in the model.  What I would like are the variables "age:group=A", "age:group=B"
>     and "age:group=C"  (and group itself of course).  The coefficients of the model will
>     then be the age effect in group A, the age effect in group B and the age effect in C
>     rather than the standard ones of an overall age effect followed by contrasts.  These
>     is often a better format for tables in a publication.
>
>     Yes, I can reconstruct these from the original fit, but I have a lot of variables for
>     several models and it would be easier to have an automatic form.  I suspect that there
>     is an easy answer, but I don't see it.
>
>     Terry Therneau