# Select outliers with standard deviation after a nonlinear regression

I've performed an non linear regression with 3 variables and 5 parameters, using Wolfram Mathematica. Now I want to detect the outliers that are far from 2*(standard deviation) of my function. I've done a little software that investigate the outliers. But now I'm wondering if this technique has got a statistical basis. Can you help me to find this basis or some bibliography or if I can perform a non linear regression with mathematica bearing in mind the outliers? If you want I can post an example of my funcion. Thanks in advance.

• Yes, it has a statistical basis: and that basis shows your technique is not a valid way to identify outliers! If you use Mathematica's NonlinearModelFit procedure, it will give you influence measures, prediction confidence intervals, prediction standard errors, and standardized and studentized residuals: all of these are useful for identifying outliers (of various types).
– whuber
Mar 26 '13 at 14:36