Calculating RERI with Confidence Intervals for 3×2 Interaction

Sara_p-value — Sat, 20 Sep 2025 00:35:37 GMT

Hi,
I'm analyzing interaction between a categorical variable (3 levels: inadequate/adequate(ref)/excessive) and a binary medical condition on a binary outcome using modified Poisson regression with GEE.

I recoded my exposures into a joint variable with a common reference category:
Joint Exposure Categories:

0: Adequate + No medical condition (reference)
1: Adequate + Medical condition
2: Inadequate + No medical condition
3: Inadequate + Medical condition
4: Excessive + No medical condition
5: Excessive + Medical condition

Current Model:
proc genmod data=mydata;
class joint (ref='0') id [other covariates];
model outcome = joint [covariates] / dist=poisson link=log;
repeated subject=id / type=exch corrw;
run;
I want to Calculate RERI with valid confidence intervals for both exposure levels:

RERI_inadequate = RR₃ - RR₂ - RR₁ + 1
RERI_excessive = RR₅ - RR₄ - RR₁ + 1

I can extract point estimates using:
estimate 'RR01' joint 1 0 0 0 0;
estimate 'RR10_Inad' joint 0 1 0 0 0;
estimate 'RR11_Inad' joint 0 0 1 0 0;
estimate 'RR10_Exc' joint 0 0 0 1 0;
estimate 'RR11_Exc' joint 0 0 0 0 1;
ods output Estimates=rr_out;
Then manually calculate RERI point estimates. However, this doesn't provide confidence intervals for RERI.
Questions:

Is my ESTIMATE statement approach correct for extracting the individual RRs?
What's the best method to get confidence intervals for RERI and how to code?

topic Calculating RERI with Confidence Intervals for 3×2 Interaction in SAS Programming

Calculating RERI with Confidence Intervals for 3×2 Interaction