Hi there,
I ran genmod on a binary DV, and I was puzzled that the parameter for my "time2" variable was nonsignificant, whereas the Wald test for this same variable was significant. I show my syntax and output below. Could anyone tell me why these results differed (the other parameters matched the p values of the Wald test)? For some background, I am working with a study that consisted of 2 phases in time. The first went from 0 to 16 weeks, and the second phase went from 16 to 64 weeks. That is why I form a vector representing these time points below, because I needed to have 2 separate slopes to model the differences between these 2 differing phases.
data ham;
set ham;
*set up vectors of time points;
if time le 16 then time1 = time;
else time1 = 16;
if time gt 16 then time2 = time;
else time2 = 0;
run;
proc genmod data=ham descending;
class id hasAnxB time;
model MDD_C = time1 time2 hasAnxB time1*hasAnxB time2*hasAnxB /link=logit dist=binomial type3 wald;
repeated subject=id / within=time corrw type=un;
run;
The GENMOD Procedure
Analysis Of GEE Parameter Estimates
Empirical Standard Error Estimates
Parameter Estimate S.E. Z Pr > |Z|
Intercept 1.6477 0.3973 0.8691 2.4263 4.15 <.0001
time1 -0.1792 0.0302 -0.2383 -0.1201 -5.94 <.0001
time2 -0.0021 0.0049 -0.0117 0.0074 -0.44 0.6623
HASANXB 0.00 -0.7935 0.4918 -1.7574 0.1703 -1.61 0.1066
HASANXB 1.00 0.0000 0.0000 0.0000 0.0000 . .
time1*HASANXB 0.00 0.0724 0.0392 -0.0043 0.1492 1.85 0.0644
time1*HASANXB 1.00 0.0000 0.0000 0.0000 0.0000 . .
time2*HASANXB 0.00 -0.0269 0.0107 -0.0478 -0.0059 -2.52 0.0119
time2*HASANXB 1.00 0.0000 0.0000 0.0000 0.0000 . .
Wald Statistics For Type 3 GEE Analysis
Source DF Square Pr > ChiSq
time1 1 53.31 <.0001
time2 1 8.50 0.0036
HASANXB 1 2.60 0.1066
time1*HASANXB 1 3.42 0.0644
time2*HASANXB 1 6.33 0.0119
Message was edited by: mburns
Message was edited by: mburns
Message was edited by: mburns
Message was edited by: mburns
Message was edited by: mburns