针对费率运行GEE模型，并使用也是费率的协变量进行调整（GENMOD SAS）

Question

I want to run a GEE for clustered data - I am trying to get incidence rate ratios (IRR) for antibiotic reactions between two drugs. I have searched for information on constructing GEE models (GENMOD in SAS, xtgee in Stata) but I can't find criteria on what type of variables can be included as covariates. My model is this:

 proc genmod data = mydata;
  class Pt fev1_cat;
  model rate_pip = cumulative_dose_before fev1_cat Average_Dose_Admis mero_rate  / 
  type3 dist=poisson link=log;
  repeated subject=Pt;
 run;

rate_pip is the rate of adverse events (AE) for antibiotic in question, mero_rate is the rate of AE for a different antibiotic. The other variables are either categorical or continuous.

if I adjust the GEE with a covariate that is a rate, is it 1) a correct use of the GEE model, and 2) would the interpretation of the exp(coef) be the IRR between the two rates of AE, or is it interpreted as: for each unit increase in rate of mero_rate, the IRR of rate_pip is x times higher/lower?

Thanks - I'd be happy to clarify/provide more info if needed.

Answer 1

I can't say whether this is a correct use of a GEE model without knowing a little more about the data structure, but I don't know of anything that's special about GEE models that would preclude the use of rate variables as predictors (as compared to say a ordinary least squares regression model). If the model is okay without the mero_rate predictor, it would probably be okay with it too. Maybe the caveat is that it can't be too correlated with the other predictors.

As far as interpretation goes, I think you've pretty much got it. The log of the incidence rate increases by beta units for a mero_rate value of x+1 events per unit time, compared to a mero_rate value of x events per unit time, all other things equal.