Hi, I am trying to figure out how to conduct a difference in difference analysis with a proc Genmod. My outcome is a continuous variable (Y), and I would like to know if being a case (Yes/no) influences this outcome. I have repeteated measures ( time = 0 to 12), and several not time-dependent variables (Adj_var). My code : PROC GENMOD DATA=GEE_PREPARATION2;
CLASS id time(ref="0") Adj_var (ref="0") case(ref="0") / param=ref;
MODEL Y= case time Adj_var case*time;
REPEATED SUBJECT=id / TYPE=UN CORRW; RUN; And... I don't understand my results at all. For time*Case (1 1) it gives me a coefficient "22.8271". I thought it was the result of my Diff in Diff because it's the same results when I calculate it by hand DiD=[(Y11 - Y10)-(Y01-Y00)]. But he didn't take into account my adjustment variables (Adj_var). If I try with this code : PROC GENMOD DATA=GEE_PREPARATION2; CLASS id time(ref="0") case(ref="0") / param=ref; MODEL ville= case time case*time; REPEATED SUBJECT=id / TYPE=UN CORRW; RUN; I have the same results. I must have missed something, but I don't see what...
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