{smcl}
{* 5mar2004}{...}
{hline}
help for {hi:ppplot}
{hline}

{title:P-P plots} 

{p 8 17 2} 
{cmd:ppplot}
{it:plottype} 
{it:varname}
[{it:weight}] 
[{cmd:if} {it:exp}] 
[{cmd:in} {it:range}]
{cmd:,}
{cmd:by(}{it:byvar}{cmd:)}
[ 
{cmdab:miss:ing}
{cmdab:ref:erence(}{it:#}{cmd:)} 
{it:graph_options}
]

{p 8 17 2}
{cmd:ppplot} 
{it:plottype} 
{it:varlist}
[{cmd:if} {it:exp}] 
[{cmd:in} {it:range}]
[{cmd:,}
{it:graph_options}
]


{title:Description}

{p 4 4 2}{cmd: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 {it:byvar}. 

{p 4 4 2}For more than one variable in {it:varlist}, only observations with all
values of {it:varlist} present are shown.

{p 4 4 2}The plot may be one of eight {help graph_twoway:twoway} types, namely,
{cmd:area}, {cmd:bar}, {cmd:connected}, {cmd:dot}, {cmd:dropline}, {cmd:line},
{cmd:scatter} or {cmd:spike}. The {it:plottype} must be specified. 

{p 4 4 2}{cmd:fweight}s and {cmd:aweight}s may be specified. 


{title:Options}

{p 4 8 2} {cmd:by(}{cmd:)} specifies that groups are defined by the 
distinct values of a single variable {it:byvar}. {cmd:by()}
is only allowed with a single {it:varname}.

{p 4 8 2}{cmd:missing}, used only with {cmd:by()}, permits the use of
non-missing values of {it:varname} corresponding to missing values for the
variable named by {cmd:by()}. The default is to ignore such values.

{p 4 8 2}{cmd:reference()}, used only with {cmd:by()}, specifies a reference 
group as a value of {it:byvar}. By default, the highest value of {it:byvar} 
in the data specified defines the reference group. 

{p 4 8 2}{it:graph_options} refers to options of {help graph} appropriate to
the {it:plottype} specified.  


{title:Examples}

{p 4 8 2}{inp:. ppplot connected mpg, by(foreign)}{p_end}
{p 4 8 2}{inp:. ppplot connected mpg, by(foreign) ref(0)}{p_end}
{p 4 8 2}{inp:. ppplot connected mpg, by(foreign) plot(function y = x, clp(dash))}{p_end}
{p 4 8 2}{inp:. ppplot connected width length}{p_end}

{p 4 4 2}To sample all possible {it:plottype}s: 

{p 4 8 2}{inp:. foreach t in area bar connected dot dropline line scatter spike {c -(}}{p_end}
{p 4 8 2}{inp:. {space 8}ppplot `t' mpg, by(foreign)}{p_end}
{p 4 8 2}{inp:. {c )-}}

{p 4 4 2}Some tuning may be desirable, for example:: 

{p 4 8 2}{inp:. ppplot bar mpg, by(foreign) bartype(spanning) base(0)}


{title:Author}

{p 4 4 2}Nicholas J. Cox, University of Durham{break} 
n.j.cox@durham.ac.uk
	 

{title:Also see}

{p 4 13 2}On-line: help for {help graph}, {help cumul}, {help distplot} 
(if installed)

{p 4 13 2}Manual: {hi:[G] graph}, {hi:[R] cumul}, {hi:[R] diagnostic plots}