# $\chi^2$ parameter of a data fit

So what is that parameter. When I make a non-linear fit, the program gives me a value χ2/doF. What is it?

I know some statistics and I know those χ2 distributions are used for non-parametric contrasts, like how good a fit is to a data, knowing that λ⇝χ2n−1 (that's supposed to mean the pearson parameter behaves like that distribution). I suspect it's totally related to that, telling me how good the fit is actually making the contrast, I don't know though, how to relate that value, as I'm not giving aconfidence level, so I guess it's a general number something independent of that so you decide if it's good or not, what is it exactly? Why is it divided by the degrees of freedom?

Thanks

• Because there are many ways to "make a nonlinear fit," please provide some details of what you are doing, including what program you are using. (Doesn't the program's documentation explain its output?)
– whuber
Mar 21, 2013 at 17:47
• @whuber I'm using SciDavies. And I'm fitting to an arbritary function (not linear) to a set of points. I searched the documentation and didn't find anything. The algorithm it says it's using is Levenberg-Marquardt Mar 21, 2013 at 18:47