topic Re: Gee Reference group in SAS Procedures

Gee Reference group

alexisn1 — Wed, 03 Apr 2019 14:16:25 GMT

Hi,

I am trying to run a Proc gee for a multinomial distribution, with a repeated statement (each id has repeated measures over visits).

This is the code that I am using:

;
proc gee data=dataset;
class id visit ygroup;
model ygroup= x/dist=multinomial link=glogit;
repeated subject=id/within=visit;
run;

The results state that "Logits modeled use '1' as the reference category.". However, looking at the Parameter Estimates for Response Model table, I am getting an intercept and estimates for groups 1 and 2 (as if it is using group '3' as the reference category).

Any ideas of why this is happening and how to fix it?

Also, I would like to use group '2' as a reference. Any ideas how to change that?

Thanks!

Re: Gee Reference group

Rick_SAS — Tue, 10 Sep 2019 13:24:37 GMT

What version of SAS are you running? In SAS v940m6, I see the message

Logits modeled use '3' as the reference category

not '1' as you report.

So that we can use the same data, I will define the Arthritis data set in the PROC GEE examples.

The following statements convert the data to look like the data you are using:

data Have;
set Arthritis;
where Rating<=3;
rename Age=x Rating=ygroup;
run;

proc gee data=have;
   class ID Visit;
   model ygroup = x / dist=multinomial link=glogit;
   repeated subject=ID / within=Visit;
run;

Please tell us what reference group is reported for these data.

As to your second question, the response variable is assumed to be ordinal, so it's not clear to me that you should be changing the order. If you insist, you can recode the data or use a custom format to recode the data.

Re: Gee Reference group

pau13rown — Wed, 11 Sep 2019 18:26:06 GMT

use proc genmod and specify "param=ref ref='2'" in the class statement?

Re: Gee Reference group

MichaelL_SAS — Thu, 12 Sep 2019 18:10:09 GMT

You might want to follow up with Technical Support at SAS regarding this issue. If I recall this was a bug in SAS 9.4M3 (SAS/STAT 14.1). The information in the Parameter Estimates table is correct, there was an error in the response profile message and the REF= option as a response variable option was not supported. These issues were fixed starting in SAS 9.4M4 (SAS/STAT 14.2).

Re: Gee Reference group

alexisn1 — Thu, 12 Sep 2019 18:21:37 GMT

Thank you for your reply.

I ran the exact model in my SAS and got the following in my results: Logits modeled use '1' as the reference category.

The Parameter Estimates were given for ygroups 1 and 2.

It seems, that as stated below, there is a bug in SAS, as I am using SAS version 14.1.

Thanks Again!

Alexis

Re: Gee Reference group

alexisn1 — Thu, 12 Sep 2019 18:22:34 GMT

I am using version SAS 14.1, thus it may actually be a bug in my SAS.

Thank you!

Alexis