Quantile plot -------------
^quantil2^ varname [^if^ exp] [^in^ range] [^, r^everse ^rank^s graph_options ^a(^#^) by(^byvar^) miss^ing ]
^quantil2^ varlist [^if^ exp] [^in^ range] [^, r^everse ^rank^s graph_options ^a(^#^)^ ]
Description -----------
^quantil2^ produces a plot of the ordered values of varlist against the so-called plotting positions, which are essentially quantiles of a uniform distribution on [0,1] for the same number of values, or optionally the so-called unique ranks.
For n values of a variable x ordered so that
x[1] <= x[2] <= ... <= x[n-1] <= x[n]
the plotting positions are (i - a) / (n - 2a + 1) for i = 1, ..., n. The unique ranks run 1 to n, tied values being allocated different ranks so that each integer is assigned to a value.
For more than one variable in varlist, only observations with all values of varlist present are shown.
Options -------
^reverse^ reverses the sort order, so that values decrease from top left. Ordered values are plotted against 1 - plotting position or _N - rank + 1.
^ranks^ specifies the use of ranks rather than plotting positions.
graph_options are options allowed with ^graph, twoway^.
Note that with ^by( )^ each function is treated graphically as if it were a separate variable.
^a(^#^)^ specifies a in the formula for plotting position. The default is a = 0.5, giving (i - 0.5) / n. Other choices include a = 0, giving i / (n + 1), and a = 1/3, giving (i - 1/3) / (n + 1/3).
^by(^byvar^)^ specifies that calculations are to be carried out separately for each class defined by a single variable ^byvar^. Any graph will, however, show the functions for all classes. ^by(^ ^)^ is only allowed with a single varname.
^missing^, used only with ^by( )^, permits the use of non-missing values of varname corresponding to missing values for the variable named by ^by( )^. The default is to ignore such values.
Remarks -------
^quantil2^ uses ^egen ... = pp(...)^ to calculate plotting positions. ^_gpp.ado^ should be installed in your personal ado directory or folder.
Examples --------
. ^quantil2 mpg^ . ^quantil2 mpg, by(foreign)^ . ^quantil2 mpg trunk hdroom, rescale^
Author ------
Nicholas J. Cox, University of Durham, U.K. n.j.cox@@durham.ac.uk
Also see --------
On-line: help for @graph@, @quantile@, @distplot@ (if installed), @egen@ Manual: [R] graph