Controlling for variable

[yael]

Hello

I am writing after trying to understand it, also asked in SAS programming (by mistake) and got the attached answer.

My question is - I want to use PROC MIXED as I have fixed effect and also random effects in my model. Which statement in SAS reprents the CONTROL VARIABLES in my model? is this the CLASS statement?

The answer I got from the gentelman is:

Questions like this are better suited for the Statistical Procedures forum.

You should start by reading the entire chapter on PROC MIXED.  The CLASS statement is for identifying variables that are represented by levels (e.g. race) rather than on a continuium (e.g. age); this is the way that the CLASS statement is used in all of the SAS stat procedures.

"Control" variables are another type of independent variable.  The SAS procedures don't treat them any differently, but the analyst thinks about them differently.  I see the term most often in epidemiology.  They are usually independent variables that effect the outcome but aren't the topic of interest in the analysis (e.g. In a general regression framework, someone might want to "examine the effect of BP on heart rate controlling for age.").  In MIXED, most control variables are fixed effects.

Finally- Can you help me by telling me which topics I have to read in order to find more knowledge on control variables in SAS (especially in PROC MIXED)

Thanks a lot for any help:

[Reeza · Accepted solution]

For starters read the documentation. 

https://support.sas.com/documentation/cdl/en/statug/63033/HTML/default/viewer.htm#statug_mixed_sect0...

The previous answer is correct, a CONTROL variable is an independent variable which can be continuous or categorical. 

The term CONTROL variable doesn't really exist within SAS. Is there something specific you're looking for, with regards to the variable/analysis?