Dear Clive Nicholas,
In the archives, I found a post which seems relevant.
http://www.stata.com/statalist/archive/2003-07/msg00193.html
A portion of your mail (At 03:52 04/08/14 +0100) says,
>
> >From my own practical experience, variables tend to be dropped for three
> main reasons:
>
> (a) they are co-linear with one or more other independent variable(s);
> (b) they are one of a set dummy variables, one of which has to be left out
> to serve as a comparison group; or
> (c) they simply don't vary enough across observations to be variables!
>
> Others, I'm sure, could give more precise, mathematical explanations as to
> why variables are dropped from regressions; and, indeed, there may be
> other good commonsense reasons. But these, to me, are the most common.
>
Anyway, impressive and/or practically thankful mails seem to
be classified into:
(a) deep information from the company staffs
(b) conversations between expert statisticians (most of these
I cannot understand, though)
(c) answers of the Stata gurus to questions of beginners.
I really thank to the statalist and contributers for this,
and hope such mails come out further.
Toyoto
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