simple interactions
Dear Terry, Does fitting group + age:group instead of age*group solves your problem? Best regards, ir. Thierry Onkelinx Instituut voor natuur- en bosonderzoek / Research Institute for Nature and Forest team Biometrie & Kwaliteitszorg / team Biometrics & Quality Assurance Kliniekstraat 25 1070 Anderlecht Belgium To call in the statistician after the experiment is done may be no more than asking him to perform a post-mortem examination: he may be able to say what the experiment died of. ~ Sir Ronald Aylmer Fisher The plural of anecdote is not data. ~ Roger Brinner The combination of some data and an aching desire for an answer does not ensure that a reasonable answer can be extracted from a given body of data. ~ John Tukey 2016-04-15 13:58 GMT+02:00 Therneau, Terry M., Ph.D. <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
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