# Find out how closely the model fits the data

I have an interpolating function

pfun[t]


and a data set in the form of

{{t,f}}


what can I do to get a numeric estimate on how closely the function fits the data ?

I read up on how LinearModelFit/NonlinearModelFit has options to display r-squared value, but this doesn't suit my case as I already have a function and don't need to fit anything.

 (pfun[#[[1]]]-#[[2]])^2&/@data //Total