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Re: st: RE: -ciplot- and multiple by options


From   "Sergiy Radyakin" <serjradyakin@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: -ciplot- and multiple by options
Date   Tue, 9 Oct 2007 13:07:20 +0200

Thank you Nick,

the reason that I didn't mention that -ciplot- is a user-written
command was that I somehow was sure that the author of -ciplot- will
see the post and reply (and I was right :). I now see how the multiple
"by()" options are working in -ciplot- and thanks to your advice
external command -stripplot- seems to be doing, what I wanted:

stripplot price, over(rep78) by(foreign) bar msymbol(none) vertical

I don't see it "silly", though, to plot the confidence intervals for
the means of the cell data, defined by two variables.

Best regards, Sergiy



On 10/8/07, Nick Cox <n.j.cox@durham.ac.uk> wrote:
> The Statalist FAQ advises, as good practice, saying where
> non-official commands come from. -ciplot- is a user-written
> command on SSC.
>
> The help for -ciplot- starts like this:
> -------------------------------------------------------------------------
>
> Plots of confidence intervals
>
>        ciplot varlist [if exp] [in range] [weight] [, by(byvar)
>                 missing ci_options [horizontal | vertical]
>                 rcapopts(rcap_options) scatter_options]
>
>
> Description
>
>    -ciplot- produces a display of means and confidence intervals.  Means
>    are shown by point symbols and intervals by capped bars.  -ci- is
>    used for the calculations.  -aweights- and -fweights- are allowed; see
>    help on -weights-.
>
>
> Options
>
>    -by()- defines a grouping variable, which is treated as categorical,
>        not measured.
>
>    [...]
>
>    scatter_options refers to options of graph twoway scatter.
> ----------------------------------------------------------------
>
> and inside -ciplot- there is a standard -syntax- statement
>
>
>        syntax varlist(numeric) [if] [in] [aweight fweight]        ///
>        [ , BY(varname) LEVel(integer $S_level) Poisson BINomial   ///
>        Exposure(varname) EXAct Jeffreys Wilson Agresti Total      ///
>        Total2(str asis) MISSing INCLusive                         ///
>        YTItle(str) XTItle(str)                                    ///
>        HORizontal VERTical RCAPopts(str asis) plot(str asis) * ]
>
> As far as -ciplot- is concerned -by()- needs a varname (not varlist),
> as Sergiy reports.
>
> So why can he get away with specifying two -by()- options? It
> is not in general illegal to specify an option twice, and as from
> Stata 8 much use is made of that in graphics.
>
> In this case, what happens with two -by()- options is that the
> first becomes the -by()- specified explicitly in the -syntax- and
> the second gets smuggled past the border wrapped up in the
> wildcard *.
>
> -ciplot, by()- was intended to echo -ci, by()- when the latter
> was part of -ci-'s standard syntax. (Now the overt syntax is
> to use -by ...: ci- but a -by()- option is still allowed.)
> This option never had a graphical role.
>
> As the help above implies, -ciplot- does two main things,
> fire up -ci- to get confidence intervals and then fire
> up -graph- to plot them. If you go with the auto data
>
> ciplot price, by(rep78) by(foreign)
>
> then -by(rep78)- is used in calculating
> confidence intervals and -by(foreign) is used
> in plotting them. The results will look odd
> and in effect you will get a silly answer
> to a silly question.
>
> I don't feel especially inclined, however, to regard this as a
> bug, as any user doing this is trying something way
> beyond the documentation and should expect the
> possibility of strange consequences. There may be nested
> categorical variables for which this is
> an undocumented way of getting a reasonable graph.
>
> I suspect that -ciplot- has climbed to the end
> of its branch of the evolutionary tree. A more
> versatile command is -stripplot- from SSC.
> Alternatively, use -egen, group()- before
> using -ciplot-.
>
> Nick
> n.j.cox@durham.ac.uk
>
> Sergiy Radyakin
>
> > In -ciplot- I can not specify multiple variables in the "by()" option,
> > but I can specify multiple "by()" options each with one variable. I
> > wonder if ciplot is supposed to work like this?
> >
> > The results look quite strangely [Stata v9.2, Windows]:
> >
> >    sysuse auto
> >    ciplot price, by(foreign) by(rep78)
> >
> > or even like this:
> >
> >    ciplot price, by(rep78) by(foreign)
> >
> > Is there any deep statistical motivation for not allowing such graphs?
> > or is it just bug?
> >
> > In any case the above graphs look misleading, when confronted
> > with the data:
> >
> >    table rep78 foreign, c(mean price sd price)
> >
> > Am I missing something?
>
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