RE: st: Several quantile plots in one diagram

["Nick Cox" <n.j.cox@durham.ac.uk>]

Barbro is talking about -quantil2-, later renamed -qplot, written by
myself. The searchable documentation makes the line of succession clear,
so I do not know why there is any uncertainty on this point. 

. search quantil2

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SJ-6-4  gr42_4  . . . . . . . . . . . . . . . . . .  Software update for
qplot
        (help qplot if installed) . . . . . . . . . . . . . . . . .  N.
J. Cox
        Q4/06   SJ 6(4):597
        better handling of x-axis titling, a new option allowing
        the user to specify an alternative plotting position or
        rank variable

SJ-5-3  gr42_3  . . . . . . . . . . . . . . . . . .  Software update for
qplot
        (help qplot if installed) . . . . . . . . . . . . . . . . .  N.
J. Cox
        Q3/05   SJ 5(3):471
        simplified syntax; both by() and over() are now allowed

SJ-4-1  gr42_2  Software update for Quantile plots, generalized; renamed
qplot
        (help qplot if installed) . . . . . . . . . . . . . . . . .  N.
J. Cox
        Q1/04   SJ 4(1):97
        software update for quantil2, now renamed qplot

STB-61  gr42.1  . . . . . . . Quantile plots, generalized: update to
Stata 7.0
        (help quantil2 if installed)  . . . . . . . . . . . . . . .  N.
J. Cox
        5/01    pp.10--11; STB Reprints Vol 10, pp.55--56
        updated for use with Stata 7

STB-51  gr42  . . . . . . . . . . . . . . . . . .  Quantile plots,
generalized
        (help quantil2 if installed)  . . . . . . . . . . . . . . .  N.
J. Cox
        9/99    pp.16--18; STB Reprints Vol 9, pp.113--116
        generalizes the quantile command by allowing more than one
        variable (or a by() option), more graphical choices, general
        plotting positions, and an option to reverse the order

-quantil2- is indeed "pretty old". What's not explicit in this thread is
that it produces the old graphics, for Stata 7 or less. It doesn't crash
my more modern versions of Stata. -qplot- has been available since 2004,
however.

I don't understand how Barbro can install -quantil2- but not -qplot-,
but no matter. I'll email her copies of the -qplot- files. 

Maarten is right: you _can_ do this yourself. For related advice in the
same spirit, see

SJ-7-2  gr0027  . .  Stata tip 47: Quantile-quantile plots without
programming
        . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N.
J. Cox
        Q2/07   SJ 7(2):275--279                                 (no
commands)
        tip on producing various quantile-quantile (Q-Q) plots

I disagree with Martin about recommending official -quantile- here.
-quantile- can only very awkwardly handle two or more groups; you might
as do it all yourself. 

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

Widerstedt Barbro

Thank you, that worked very well, but does this mean that the lazy-girl,
no-think option is not available then :) ? 

Maarten buis

--- On Wed, 21/4/10, Widerstedt Barbro wrote:
> I have a panel dataset with 6 years, and I would like to
> plot the distribution of a variable in a quantile plot
> for each year in this panel. I have installed quantil2,
> which causes Stata to shut down when I try to save the
> graph. There seems to be upgrades (quantil2 is pretty
> old), but because of firewall restrictions on the remote
> workstation where Stata resides, I can't search or
> install from STATA. I can't find the update qplot or
> other updrage mentioned in e.g. Stata Journal
> 2006(4) on SSC. Where can I find this functionality? 
> (I use Stata 10) 

You can always recreate the graph from first principle.
In the example below I assume you want to display these
distribution in the same plot. This plot is basically
just a scatter plot. All you need to do is create the
so called "plotting positions", that is, the values on
the x-axis. This is discussed in this Stata FAQ:
<http://www.stata.com/support/faqs/stat/pcrank.html>

In the example below the rep78 variable takes the
place of your year variable.

*-------------- begin example ---------------------
sysuse auto, clear
recode rep78 1/2=3

// create plotting positions
gen byte mis = missing(price,rep78) 
bys rep78 mis (price) : gen int i = _n if mis == 0
bys rep78 mis         : gen int n = _N if mis == 0
gen hazen = (i - .5) / n

twoway scatter price hazen if rep78 ==3 || ///
       scatter price hazen if rep78 ==4 || ///
       scatter price hazen if rep78 ==5,   ///
       legend(order(1 "Average"            ///
                      "or worse"           /// 
                    2 "Good"               ///
                    3 "Excellent" ))       ///
       xtitle("fraction of the data")      ///
       ytitle("quantiles of price")
*--------------- end example ------------------------
(For more on examples I sent to the Statalist see: 
http://www.maartenbuis.nl/example_faq )


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