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P-P plots

ppplotplottypevarname[weight] [ifexp] [inrange],by(byvar)[missingreference(#)graph_options]

ppplotplottypevarlist[ifexp] [inrange] [,graph_options]

Description

ppplotproduces 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 ofbyvar.For more than one variable in

varlist, only observations with all values ofvarlistpresent are shown.The plot may be one of eight twoway types, namely,

area,bar,connected,dot,dropline,line,scatterorspike. Theplottypemust be specified.

fweights andaweights may be specified.

Options

by()specifies that groups are defined by the distinct values of a single variablebyvar.by()is only allowed with a singlevarname.

missing, used only withby(), permits the use of non-missing values ofvarnamecorresponding to missing values for the variable named byby(). The default is to ignore such values.

reference(), used only withby(), specifies a reference group as a value ofbyvar. By default, the highest value ofbyvarin the data specified defines the reference group.

graph_optionsrefers to options of graph appropriate to theplottypespecified.

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)

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

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

Manual:

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