Is there any way to get an estimate of the goodness of fit from FindFit, for instance getting the final error? The documentation doesn't provide any hints, and a quick Google search didn't return any useful link either. Am I missing something obvious?

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    $\begingroup$ A discussion of quantifying the quality of fits, including the error residuals, appears here: tutorial/StatisticalModelAnalysis. $\endgroup$ – David G. Stork Dec 9 '14 at 17:15

You can use NonlinearModelFit instead of FindFit.

dt = Table[Prime[x], {x, 20}];
FindFit[dt, a x Log[b + c x], {a, b, c}, x]
(* {a -> 1.42076, b -> 1.65558, c -> 0.534645} *)

nlm = NonlinearModelFit[dt, a x Log[b + c x], {a, b, c}, x];
(* 1.42076 x Log[1.65558+0.534645 x]*)


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Grid[Transpose[{#, nlm[#]} &[{"AdjustedRSquared", "AIC", "BIC", "RSquared"}]], Alignment -> Left]

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See: NonlinearModelFit >> Properties >> Goodness of fit measures

  • $\begingroup$ Two tiny questions if I may: -1- I am using nlm["ParameterTable"] as well after a nonlinearModelFit, but I get a warning that `"The property values {"ParameterTable"} assume an unconstrained model..." probably because I added a constraint while fitting, has this happened to you as well? -2- Is there a built-in way of also estimating the chi-squared per degree of freedom for the fit? Many thanks in advance. $\endgroup$ – user52181 Jun 17 '19 at 10:53
  • $\begingroup$ You can use NMinimize function for fitting. Just minimize chi-square_nu over the parameter space to find your parameters. $\endgroup$ – OkkesDulgerci Aug 29 '19 at 4:38

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