Multilevel model proc glimmix how to define reference group for predictors when old SAS

[stmaatta]

Hi,

I am trying to do multilevel analysis by using Proc Glimmix and applying this: https://support.sas.com/resources/papers/proceedings15/3430-2015.pdf

Anyhow, I have multiple dichotomous explanatory factors, and I need to specify the reference groups for those. I have used the tips provided here: https://support.sas.com/kb/37/108.html 

and aiming to use the sort option. I have older version of SAS, so setting reference for class (ref=class) is not option. 

My problem is that I have been able to sort right reference groups for most of the explanatory factors, but there are still few left that it is not read right. I have tried to set them with or without descending option and tried different ways to set the right reference group without succeeding. Is there any tips what I could do or try? 

Here is example of code. Of this example, all other explanatory factors are read right expect ind_fm and ind_wh. They does not work either then if I define "descending" in the front. 

proc sort data=od out=New;
by
descending sp
descending im2
am2
school_level
ind_sd
ind_hm
ind_fm
ind_bn 

ind_hw
ind_dp

kK;

run;

PROC GLIMMIX DATA=new METHOD=LAPLACE NOCLPRINT
order=data;
CLASS

sp
 im2
am2
school_level
ind_sd
ind_hm
ind_fm
ind_bn 

ind_hw
ind_dp

kK;
MODEL ind_ls (EVENT=LAST) =
sp
 im2
am2
school_level
ind_sd
ind_hm
ind_fm
ind_bn

ind_hw
ind_dp / CL DIST=BINARY
LINK=LOGIT SOLUTION ODDSRATIO (DIFF=FIRST LABEL);
RANDOM INTERCEPT / SUBJECT=kK TYPE=VC SOLUTION CL;
COVTEST / WALD;
run;

Thank you for all the help you can provide!

[sbxkoenk]

Hello,

What version of SAS do you have?
Submit :

%PUT &=sysvlong4;

to find out (and send us what it displays in the LOG).

I think you must have a very old SAS if it does not support

REF=’level’ | FIRST | LAST

on the variables you specify in the CLASS statement.

Use that REF= between brackets right after specification of your dichotomous explanatory variable.
Like here :

CLASS Statement

CLASS variable <(REF= option)> …<variable <(REF= option)>> </ global-options>;

Koen

[stmaatta]

Thank you for the reply. My SAS version is 8.3 Update 3 (8.3.3.181) (64-bit).

I tried once again with REF-option in Class statement, and I noticed that it seems to work just fine with dichotomous predictors, but not if I have three classes or more. For instance, I have predictor variable called education, and it has 3 classes (low, middle and high). I would like to use high as my reference category. And when I define it with class ref-option, it sets the middle-class as reference. The same thing happens with other variables that have 3 or more classes (e.g. perceived income, or family living arrangements) It does not recognise the right reference group. Any tips for that?

[sbxkoenk]

SAS v8. Phew 😉.
( SAS 9.2 was released in March 2009 )

I think the best you can do is recode your levels to a numeric (1,2,3 ...).
Then apply a format to the numbered levels (to see the original string value).

When choosing a reference level, SAS v8 will take the internal value (AFAIR) and it will be the first or the last level (AFAIR).

Cheers,

Koen

[StatsMan]

The last v8 release was over 20 years ago (March, 2001). There have been many, many advances in mixed models since that release beyond REF= for specifying reference levels for CLASS effects. If you can find a newer release, you will be very happy with the results you get.