Firth correction in Generalized Estimating Equations to deal with quasi-complete separation

In order to deal with complete separation in my data someone suggested that I should run penalized GEE (PGEE) by adding a Firth-type penalty term in R.

Although I have read many papers on the Firth correction, I am still not feeling comfortable that I completely understand the concept of Firth correction, as those papers require a much deeper statistical background than I have.



Can someone please explain in plain language what the firth correction exactly does?