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help for ppplot
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P-P plots 

        ppplot plottype varname [weight] [if exp] [in range] , by(byvar) [
                 missing reference(#) graph_options ]

        ppplot plottype varlist [if exp] [in range] [, graph_options ]


Description

    ppplot produces a P-P (probability-probability) plot of the cumulative
    distribution functions of one or more groups or variables against that of
    a reference group or variable, for the same sets of observed values. By
    default the reference group is the last variable named, or, with a single
    variable, that defined by the highest value of byvar.

    For more than one variable in varlist, only observations with all values
    of varlist present are shown.

    The plot may be one of eight twoway types, namely, area, bar, connected,
    dot, dropline, line, scatter or spike. The plottype must be specified.

    fweights and aweights may be specified.


Options

    by() specifies that groups are defined by the distinct values of a single
        variable byvar. 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.

    reference(), used only with by(), specifies a reference group as a value
        of byvar. By default, the highest value of byvar in the data
        specified defines the reference group.

    graph_options refers to options of graph appropriate to the plottype
        specified.


Examples

    . ppplot connected mpg, by(foreign)
    . ppplot connected mpg, by(foreign) ref(0)
    . ppplot connected mpg, by(foreign) plot(function y = x, clp(dash))
    . ppplot connected width length

    To sample all possible plottypes:

    . foreach t in area bar connected dot dropline line scatter spike {
    .         ppplot `t' mpg, by(foreign)
    . }

    Some tuning may be desirable, for example::

    . ppplot bar mpg, by(foreign) bartype(spanning) base(0)


Author

    Nicholas J. Cox, University of Durham
    n.j.cox@durham.ac.uk


Also see

    On-line: help for graph, cumul, distplot (if installed)

    Manual: [G] graph, [R] cumul, [R] diagnostic plots