# Studentized residuals and goodness-of-fit with robust linear regression

Could you please advise whether studentized residuals are meaningful when computed on a robust linear regression model using an M-estimator?

I'd like to use it to detect outliers by doing something like this:

rfit = rlm(y~x, data=d)
pt(rstudent(rfit), df=nrow(d)-3)


Is this reasonable? I'd be quite happy with a rather crude measure and I'd rather err on the conservative side.

I'm also wondering whether I should run some kind of diagnostic of the general goodness of fit on this robust model before doing this.

• Have a look at the fit.models function in the fit.models package. This provides a comparison of regression diagnostics of model fits using lm and rlm. – Tony Ladson Feb 8 '16 at 2:41