topic Logistic procedure: reference group in SAS Procedures

Logistic procedure: reference group

bncoxuk — Thu, 14 Jul 2011 15:56:15 GMT

Hi,

I used the program below with the purpose of setting age group 15 as the reference group for comparison. But the result shows that age group 9 has been set as the reference group. Don't understand where is the problem?:smileyconfused:

PROC LOGISTIC DATA=work.test;
CLASS age (PARAM=REF REF='15') sex /param=GLM;
MODEL score=age sex /AGGREGATE SCALE=NONE;
OUTPUT OUT=work.test02 pred=pred reschi=reschi;
RUN;

Result:

age1
age10
age11
age2
age3
age4
age5
age6
age7
age8
age9: 0

Logistic procedure: reference group

data_null__ — Thu, 14 Jul 2011 17:05:03 GMT

Do you have an age group 15?

Logistic procedure: reference group

bncoxuk — Thu, 14 Jul 2011 20:11:26 GMT

Hi data_null, there is no age group 15.

Probably the reason why the setting of reference group failed to work is because the GLM? I checked SAS procedure manual, which indicates that when there is /param=GLM, the manual specification of reference group will not work.

Does it mean that if I really prefer the GLM matrix, there is no way that I can choose my preferred reference group?

Logistic procedure: reference group

data_null__ — Thu, 14 Jul 2011 22:04:02 GMT

Does it mean that if I really prefer the GLM matrix, there is no way that I can choose my preferred reference group?

The group that comes last when the values of the CLASS variables are ordered, depending on the value of ORDER= class statement option, will be the reference group when PARAM=GLM.

You can recode or reFORMAT the value to achieve the order you desire.