[R-sig-ME] treating measurement occasions as a numerical or as a factor predictor

[Rich Shepard]

On Sun, 13 Dec 2015, K Imran M wrote:

> I would like to ask a question about treating measurement occasions in a
> longitudinal analysis specifically when using linear mixed model. In my
> study, I have taken data on 3 separate occasions (at baseline, at 1 month
> and at 3 months post baseline). I am not sure what is best approach treat
> these measurement occasions in my analysis using lmer or lme functions.
> Should I treat them as a numeric or as a factor variable. My feeling says
> that I should treat such measurement occasions as a factor but I do not
> have strong theoretical reasons for that.

Kamarul,

   What question do you want to answer with your data?

Rich