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Re: st: xtsum formulas


From   "Sebastian F. Büchte" <sfbuechte@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: xtsum formulas
Date   Thu, 6 Jul 2006 15:55:53 +0200

Since I am always excited about learning new things, I tried
viewsource xtsum.ado. Everything worked nicely, but I found the
following nine lines at the end of the ado-file and I am wondering why
they are there.

. sum cost avgcost dcost

Variable         |      Mean   Std. Dev.       Min        Max |    Observations
-----------------+--------------------------------------------+----------------
----+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
longlong overall | 123456789  123456789      3.154     191.56 |     N =12345678
longlong overall |  44.44588   46.30909      3.154     191.56 |     N =12345678
        between |             44.57574     4.4645    125.584 |     n =      22
        within  |             20.41346  123456789  912345678 | T-bar =       6

It is not a critical thing to know but I am just curious.

Regards,
seb


On 7/6/06, Nick Cox <n.j.cox@durham.ac.uk> wrote:
Quite so. Indeed, knowing that -xtsum- is implemented as an .ado file
(strictly, not a .do file) means that

viewsource xtsum.ado

will give you a view of the code, without (a) needing
to doing a -which- to find out precisely where the
file is, or (b) any risk of modifying the code.

This tip is explained in more detail in

SJ-6-1  pr0022  . . . . . . . . . . . Stata tip 30: May the source be with you
       Q1/06   SJ 6(1):149--150                                 (no commands)
       tip for using viewsource to locate and view source
       code or text files

and in "Thirty-three Stata Tips" from StataCorp.

Nick
n.j.cox@durham.ac.uk

Neil Shephard

> On 7/6/06, Podestà, Federico <Federico.Podesta@amm.unitn.it> wrote:
>
> > I have (I think) a simple problem: I would like to know
> formulas used by the -xtsum- command to obtain the betweem
> standard deviation and the within standard deviation.
> > In particular I would like to know Stata code to compute
> such statistics by hand solving all parts of the formulas
> step by step.
>
> The formulas for the methods implemented in Stata (at least those I've
> ever had recourse to look up) are given in the manuals, in this
> instance it will be [XT].
>
> In this instance because -xtsum- is implemented as a do-file....
>
> . which xtsum
> /usr/local/stata9/ado/base/x/xtsum.ado
> *! version 1.0.9  06aug2004
>
> ..you can look at the code yourself by viewing the relevant file in a
> text-editor.
>
> (Be wary of modifying the file which will break things.  If you want
> to make modifications, don't, instead clone the do-file to your
> personal-ado file and rename it, and make modifications to that).

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