# Errors from a model

Hello,

when doing a extended likelihood fit using a given model (for example using a given Pdf of signal and of background, RooGaussian for example or any other), one obtain a given number of signal and background (where only Nsignal and Nbackground are floatted, all the others are fixed)

Are the errors of the fit including the errors of the modelisation of the Pdf ?

-If “yes”, how to separate the statistical error with these “systematic” modelisation of the Pdf ?

-If “no”, how to deal with computing the errors of the modelisation, apart from doing it “by hand” by making a loop to vary each parameter of the Pdf by its uncertainty ?

Would the RooKeysPdf (which is non parametrised) be a special case ?