References for methods?

Older versions of the documentation had references to methods used. Is this information now hidden somewhere? I am particularly interested in references describing curve fitting and confidence intervals for fitted parameters.

[Walter Roberson]

For which routines? 6 references for lsqcurvefit

[Stephen]

Confit

[Walter Roberson]

% Covariance matrix of fitted parameters is
%    V = inv(X'*X) * (sse/dfe)
% and the confidence intervals are
%    b +/- sqrt(diag(V)) * tinv(1-(1-level)/2, dfe)

See toolbox/curvefit/curvefit/@cfit/confint.m

[Stephen]

I was hoping for a reference to a paper or a book where this formula is derived.

[Walter Roberson]

There is a different phrasing over at stackexchange but it does not give a reference.