topic Re: Need dummy variables for Linear Regression in Statistical Procedures

Need dummy variables for Linear Regression

UGAstudent — Tue, 13 Feb 2018 23:14:45 GMT

I'm trying to run the proc genmod command, but when I look at level 3, it has 0s across the board but levels 1 and 2 have values. How do I get my level 3 data to show up? I dont know how to code for a dummy variable to get the 3rd level. Any help is appreciated!

Data UGAStudent_DATA;
Set date_difference; 

if cd4 <= 200 then cd4_levels='1';
if cd4 >=201 <=500 then cd4_levels='2';
if cd4 > 500 then cd4_levels='3'; 
run;

proc genmod data= ugastudent_data;
class cd4_levels /param=glm ;
model  Factor1 =  cd4_levels n_Duration_on_ART_months ;  
run;

Re: Need dummy variables for Linear Regression

Reeza — Tue, 13 Feb 2018 23:23:21 GMT

Same answer as before. I'll move this to the Stats forum in case others want to chime in.

Re: Need dummy variables for Linear Regression

Reeza — Tue, 13 Feb 2018 23:26:45 GMT

Same answers here, for R if that helps at all with the explanation.

This is one of those cases where you need to understand the underlying statistical concepts, specifically: Degrees of Freedom, dummy coding and an over parameterized models.

Those are some key words you can use to search to explain these results.

https://community.alteryx.com/t5/Advanced-Analytics/In-the-Logistic-Regression-Report-Factor-Missing/td-p/10094

Re: Need dummy variables for Linear Regression

art297 — Tue, 13 Feb 2018 23:31:51 GMT

As others have sort of mentioned, proc genmod automatically creates dummy variables. And, with any combination of n dummy variables, all of the variance that can be explained is accounted for by n-1 of the dummy variables.

Art, CEO, AnalystFinder.com

Re: Need dummy variables for Linear Regression

Reeza — Tue, 13 Feb 2018 23:34:25 GMT

@art297 this is the previous question by the OP

https://communities.sas.com/t5/SAS-Procedures/Data-Missing-on-output/m-p/434932#M68927