I've run a GEE analysis, using the following code:

proc genmod data=b301wk descending;
  class trt pid poolct1c week;
  model rrelxw = poolct1c week trt week*trt / d=b link=logit;
  repeated subject=pid / type=cs within=week;
  estimate 'wk 1' week*trt 1  0  0  0  -1  0  0  0 trt 1 -1;
run;

All analysis runs fine, estimates are produced etc, as requested.

HOWEVER - if I changed the order the variables were specified in, in
the class statement to "  class pid poolct1c week trt;" (ie moving trt
from the beginning to the end of the class statement), then SAS could
not perform my estimate statement.

I had always thought that so long as you specify all your categorical
variables within the class statement, that the order you specified
them in, did not matter.  But the above 'phenomenon' has baffled me
and I'm sure there's a simple explanation.

Can anyone help?
TIA,
Fiona.

The order in the class statement does matter for contrasts and estimate
statements with factorial designs. It determines the order of the variables,
which variable changs fastest.

Paul R. Swank, Ph.D.
Professor, Developmental Pediatrics
Medical School
UT Health Science Center at Houston


-----Original Message-----
From: SAS(r) Discussion [mailto:SAS-L@LISTSERV.UGA.EDU] On Behalf Of F
Fordham
Sent: Thursday, April 15, 2004 6:03 AM
To: SAS-L@LISTSERV.UGA.EDU
Subject: GENMOD, GEE, CLASS statments and the order of the variables therein


I've run a GEE analysis, using the following code:

proc genmod data=b301wk descending;
  class trt pid poolct1c week;
  model rrelxw = poolct1c week trt week*trt / d=b link=logit;
  repeated subject=pid / type=cs within=week;
  estimate 'wk 1' week*trt 1  0  0  0  -1  0  0  0 trt 1 -1; run;

All analysis runs fine, estimates are produced etc, as requested.

HOWEVER - if I changed the order the variables were specified in, in the
class statement to "  class pid poolct1c week trt;" (ie moving trt from the
beginning to the end of the class statement), then SAS could not perform my
estimate statement.

I had always thought that so long as you specify all your categorical
variables within the class statement, that the order you specified them in,
did not matter.  But the above 'phenomenon' has baffled me and I'm sure
there's a simple explanation.

Can anyone help?
TIA,
Fiona.