# Re: AW: st: question

 From vwiggins@stata.com (Vince Wiggins, StataCorp) To statalist@hsphsun2.harvard.edu Subject Re: AW: st: question Date Tue, 03 Nov 2009 11:28:31 -0600

```Tunga Kantarci <tungakantarci@hotmail.com> asks why, after estimation with
-regress-, -nlcom- will not work when he references values such as e(rss) and
r(df_r) in his expression.

> I wish to calculate a figure where I call coefficient estimates and
> residuals sum of squares and degrees of freedom. All these
> quantities are from the stata estimation output. When I run the
> relevant command
>
>
> I get the error "could not calculate numerical derivative". This is
> perhaps because e(rss) and e(df_r) are not estimates. (As Maarten
> pointed out yesterday actually)

The error message could be improved (and we will look into that), but the
problem is that Tunga's expression contains the estimated results e(rss) and
r(df_r), but -regress- does not estimate the standard error of those estimates
nor their covariance with _b[_cons] and _b[income].  Without those standard
errors and covariances, -nlcom- cannot estimate a standard error for Tunga's
expression.  We could argue whether e(df_r) is an estimate, but not e(rss).
-nlcom- treats all e-class results as estimates.

If Tunga does not need an estimate of the standard error then he can heed
Martin Weiss' <martin.weiss1@gmx.de> advice and type,

If Tunga wants standard errors and wants to treat e(df_r) as fixed (OK by me)
and also treat e(rss) as fixed (that gives me pause), then he can macro-expand
their values so that they become constants in his expression.

-nlcom- now sees these two values as constants and not as something from e().

-- Vince
vwiggins@stata.com

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