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Re: st: RE: Graph Bar


From   Katarina Sikavica <katarina.sikavica@unisg.ch>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: Graph Bar
Date   Wed, 28 Sep 2005 08:51:08 +0200

dear nick cox (and others),

just wanted to say: many thanks for your help! (I love statalist!)

regards from switzerland,
katy


Inactive hide details for "Nick Cox" <n.j.cox@durham.ac.uk>"Nick Cox" <n.j.cox@durham.ac.uk>


          "Nick Cox" <n.j.cox@durham.ac.uk>
          Gesendet von: owner-statalist@hsphsun2.harvard.edu

          27.09.2005 21:34
          Bitte antworten an
          statalist@hsphsun2.harvard.edu


An

<statalist@hsphsun2.harvard.edu>

Kopie


Thema

st: RE: Graph Bar

Katarina's data are like this:

. tab year acexist

          |        acexist
     year |         0          1 |     Total
-----------+----------------------+----------
     2000 |        29         26 |        55
     2001 |        24         61 |        85
     2002 |        69        134 |       203
     2003 |        56        152 |       208
     2004 |        50        160 |       210
-----------+----------------------+----------
    Total |       228        533 |       761

-graph bar- won't deliver the reduction she wants, at least not without
some preparation. The reason is a little technical. -graph bar- is based
mainly on a temporary reduction of the data using -collapse-, and
-collapse- doesn't offer that reduction.  (It is nearer the territory of
-contract-, but that is a different story.)

There are various solutions to the problem. A first solution is to
generate your own percent variable and then plot that directly. Each
percent is, we recall, a numerator divided by a total, multiplied by
100.

One easy way to get the total is using -egen, total()-. In Stata 8 and
earlier, the function here was -egen, sum()-, not -egen, total()-.

. egen pc = total(acexist), by(year)

. egen total = total(1), by(year)

(what's 1 + 1 + 1 + ... + 1? the total number of observations)

. replace pc = 100 * pc / total

Stata diehards would scoff at this as namby-pamby and do it with -by:-.

. bysort year: gen pc = sum(acexist)

. by year: replace pc = 100 * pc[_N] / _N

Either way, we can check that we are on the right lines by

. tabdisp year, cell(pc)

----------------------
    year |         pc
----------+-----------
    2000 |   47.27273
    2001 |   71.76471
    2002 |   66.00985
    2003 |   73.07692
    2004 |   76.19048
----------------------

Then the graph is a line away:

. graph bar (mean) pc, over(year) ytitle(percent with audit committee)
yla(, ang(h))

Or

. twoway bar pc year, ytitle(percent with audit committee)
yla(, ang(h)) barw(0.5)

Another solution employs a user-written program -catplot- from SSC. You
can install that by

. ssc install catplot

-catplot- is just a wrapper for -graph bar- (or -graph hbar- or -graph
dot-). It merely grinds through some reductions not quite trivial
otherwise and then fires up a -graph- command.

You can get a graph in one line with -catplot- without any prior
calculation, although in practice I get there through a sequence of
small experiments:

. catplot bar acexist year, percent(year) stack asyvars  yla(, ang(h))  
yti(percent without and with audit committee)
legend(order(1 "without" 2 "with"))

A graph I like more follows a reversal of coding:

. gen acexist2 = 1 - acexist

. catplot bar acexist2 year, percent(year) stack asyvars yla(, ang(h))
yti(percent with audit committee) legend(off) bar(2, bcolor(none))

The original announcement of -catplot- contains some related comment.

http://www.stata.com/statalist/archive/2003-02/msg00608.html

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

Katarina Sikavica (edited, mainly to ASCII from HTML)

I have just started with Stata graphics and have the following problem
with -graph bar-:

I have a dataset that contains data on the existence of audit committees
-acexist-. In total there are 761 companies, 533 of them having an
audit committee, 228 not. I would like to draw a -graph bar- that shows
the increase in audit committee incidence over -year-.  Drawing a -graph
bar- on the increase in the number of audit committees works fine;
however, as the data from 2000 and 2001 are of poor quality I would like
to have percentages of audit committee incidence over the years
2000-2004 (that is: 47.27% (2000); 71.76% (2001); 66.01% (2002); 73.08%
(2003); 76.19% (2004)). Neither of the following commands leads to the
desired results:

. graph bar (sum) acexist, over (year) percent
. graph bar (sum) acexist, over (year) asyvar percentages


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