Hi, I'm using ' ls.mixed ' model within Zelig to estimate causal effect of an intervention in a longitudinal study (one intervention and 8 measures after the intervention, one per year). I'm not sure to understand how to write the model in Zelig. Here's my model in written form : Level 1 : qasbatij = π0i + π1itimeij + π2itime2ij + π3itime3ij + εij Level 2 : π0i = γ00 + γ01groupi + ζ0i π 1i = γ10 + ζ1i π 2i = γ20 + ζ2i π 3i = γ30 qasbat is a continous outcome, group is the indicator of the treated and control group, I'm using polynomial time and I let the intercept and the first two polynomials to be random. In SAS, I write this model like this : proc mixed data = p_score_long method=ml noclprint covtest; class id; model qasbat = t t2 t3 group / s ddfm=bw notest; random intercept t t2 / subject=id type=un; In Zelig, I tried many formats, but Zelig seems to stall (the computing never ends). One of this format is this : z.out <- zelig(qasbat ~ group + tag(1 + t + t*t | ID), data=matched.1.mtch.long, model="ls.mixed") Within R, the group variable and the ID variable are numeric and the time variable is a factor. Merci, François Maurice Candidat à la maîtrise Département de sociologie Université de Montréal