Dear Stata users,

I have a mixed model (see the syntax below) with main effects of group (two dichotomous groups, Groepfreq and Groepbeh), and three effects for time are centered and estimated: a linear, quadratic and cubic line and interactions between them all. Two levels are estimated: measurements in participants.

What I want to know is the effect of group (Groepfreq) at day 90 (linear) or 8100 (quadratic) or 729000 (cubic). I played around with the syntax that is used to make contrasts (contrasts or margins codes) for categorial variables but it doesn't work out and I am stuck. Is it even possible to make a point estimate in a model like this? (in SPSS it is possible, but I like Stata more, so would be very happy if there is a function that can do this)

I am very curious if anybody knows.

Thank you for thinking along,
Best regards,

Sanne

code:
mixed BDI BDIbaseline i.Groepbeh i.Groepfreq c.timedayscentrkwad c.timedayscentered c.timedayscentrkub c.timedayscentrkub#i.Groepfreq c.timedayscentrkub#i.Groepbeh c.timedayscentrkwad#i.Groepfreq c.timedayscentrkwad#i.Groepbeh c.timedayscentered#i.Groepfreq c.timedayscentered#i.Groepbeh,|| ppnr:c.timedayscentered, covariance(unstructured) residuals(ma1, t(Time))

BDI baseline is a covariate
BDI is the dependent variable (8 measurements; Time in the residual covariance structure = time at point 1-8)
Other timevariables are defined as time in days (timedays)
ppnr= subject