I would like to understand why, under the OLS model, the RSS (residual sum of squares) is distributed chi square times n-p (p being the number of parameters in the model, n the number of observations).

I apologize for asking such a basic question, but I seem to not be able to find the answer online (or in my, more application oriented, textbooks).


Question: Set natbib options after loading natbib package
Answer: The \biboptions macro would seem to be set up by the elsarticle document class (or one of its subsidiary files), rather than by natbib. If you can use this command to disable sorting/compressing of numerical references, I'd do so.

The commands natbib provides to change citation-related defaults are \setcitestyle and \bibpunct. The \bibpunct command is the older of the two, and always takes exactly six arguments. The command \setcitestyle, in contrast, is more flexible and also a bit "wordier". However, neither of these two commands would allow you to undo a package option such as "sort&amp;compress".

Finally, I'd say that if you're forced to use a certain document class and bibliography style file for your journal submission, it's generally not productive to try to subvert this requirement. A cover letter, in which you explain to the editor and editorial assistants why one or more settings embedded in their journal's default setup are not chosen optimally and why they should consider accepting a different set of settings, may be the better approach to achieving a satisfactory outcome.