topic Re: Log Binomial Regression - How to compare multiple levels of a predictor in SAS Programming

Log Binomial Regression - How to compare multiple levels of a predictor

sclaire — Fri, 04 Jun 2021 15:16:46 GMT

Hello!

I am running a log binomial regression to predict relative risk of an outcome occurring (let's say Y, 0=absent, 1=present) based on a predictor (X with nominal categories 1, 2, 3, and 4). Most coding suggestions show how to do log binomial regression with a binomial predictor (not multicategorical predictor), but I want to compare RR of classes 2-4 to reference class 1. I tried the code below, but the mean estimates in the output don't entirely make sense based on my earlier ANVOA and odds ratio results. Any suggestsions?

TITLE 'UNADJUSTED X predicting Y';
proc genmod data = dataname;
CLASS X (ref="1" param=ref);
MODEL Y (event="1")= X/ dist = binomial link = log;
estimate 'Class 2' X 1/ exp;

estimate 'Class 3' X 2/ exp;

estimate 'Class 4' X 3/ exp;

run;

Re: Log Binomial Regression - How to compare multiple levels of a predictor

PaigeMiller — Fri, 04 Jun 2021 16:02:43 GMT

I don't know what your concerns are about the mean estimates, you haven't given any specifics or details, other than they don't match the ANOVA (and I would NOT expect them to match).

In PROC GENMOD, you don't need ESTIMATE statements to compute means, the LSMEANS statement gets the job done, and produces the proper error estimates.

Re: Log Binomial Regression - How to compare multiple levels of a predictor

sclaire — Fri, 04 Jun 2021 18:28:36 GMT

Thanks for the response! I am wondering if the end of my code (the estimate lines) will return what I am looking for, the RR of classes 2-4 compared to class 1 as the reference group. The reason I was unsure was because these results are not in the same direction as the ANOVA + OR. Class 1 has comparatively low % of the event occurring in the raw data yet the RR do not come out that way (even when I specify "descending").

That said, LSMEANS will give me the RR as well? Thanks again!

Re: Log Binomial Regression - How to compare multiple levels of a predictor

PaigeMiller — Fri, 04 Jun 2021 18:51:51 GMT

That depends. What does RR stand for?

LSMEANS will allow you to compare the means of the different groups.

Re: Log Binomial Regression - How to compare multiple levels of a predictor

sclaire — Fri, 04 Jun 2021 18:53:33 GMT

Risk ratio (RR) instead of odds ratio (OR)

Re: Log Binomial Regression - How to compare multiple levels of a predictor

PaigeMiller — Fri, 04 Jun 2021 20:22:16 GMT

That said, LSMEANS will give me the RR as well? Thanks again!

While I do have plenty of other experience with PROC GENMOD, but I have never done a log binomial regression, I give you this brilliant answer: try it and see.