Message-ID: <CAE5Duhsub2H6zUgNREL6m5xJ2xG6_vv-0nm2VxgFFhqD2qU0Xw@mail.gmail.com>
Date: 2021-11-13T01:32:16Z
From: Tahsin Ferdous
Subject: GEE with gamma family and log link
I am fitting a generalized estimating equation with gamma family and log
link. I am using GEE (geeglm function) from the R pcakage ?geepack? with
gamma family and log link and unstructured correlation structure.
Here, response variable or outcome is IFN_gamma_protein_pg_mg . Exposure is
intervention or probiotic use. Another covariate is Timepoint.
My code and the output is as mentioned below.
m8<geeglm(IFN_gamma_protein_pg_mg~Intervention+Timepoint,data=B,family=Gamma(link=log),id=
Participant_ID,corstr="exchangeable")
summary(m8)
* IFN_gamma_protein_pg_mg*
*Predictors*
*Estimates*
*p*
(Intercept)
0.01
*<0.001*
Intervention [Probiotics]
0.34
*0.029*
Timepoint [T2]
0.99
0.979
Timepoint [T3]
5.30
0.059
Timepoint [T4]
0.48
*0.039*
Timepoint [T5]
0.11
*<0.001*
I am trying to interpret the coefficients as follows:
For every one-unit increase in the probiotic across the population, the log
average of IFN_gamma_protein increases by 0.34 units.
The exponentiated coefficient ( exp )= (exp(0.34)=1.41) is the factor by
which the arithmetic mean outcome on the original scale multiplied, i.e.,
when intervention is probiotic, for every one-unit increase in the
probiotic across the population, the average of IFN_gamma_protein on the
original scale is 1.41 times higher compared to when intervention is
control within levels of other variable.
Similarly, for timepoint 2, the average of IFN_gamma_protein on the
original scale is exp( )= exp(0.99)= 2.69 times higher compared to
timepoint 1 within levels of other variable.
For time point 3, the average of IFN_gamma_protein on the original scale is
exp( )= exp(5.30)= 200.34 times higher compared to timepoint 1 within
levels of other variable.
Can someone confirm me that I am in the right track in the interpretation
of parameters?
I am posting here as I also want to fit a Gamma GLMM.
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