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help for chiplot                 experimental version 0.0.2, a Stata v7 program
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Chi-plot: Nonparametric Graphical Assessment of Dependence

    chiplot yvarname xvarname [if exp] [in range] [, hilite(exp) ci(#)
        sample(%) graph_options]

Description

chiplot is an experimental program implementing the nonparametric graphical
assessment of dependence plot described by N. I. Fisher and P. Switzer (see:
Graphical assessment of dependence: is a picture worth 100 tests? The American
Statistician 55(3):233-9, 2001).  Because this is offered as an experimental
program only, no details about interpretation of the plots are given; please
see the original article for guidance.  Note that the matrix form of the plot
is not implemented in this version of the program.

Options

hilite(exp) allows a logical expression to be defined to highlight a subgroup
    of data in the plot.  (This is an extension to the plot described by Fisher
    and Switzer.)

ci(#) sets p = # such that approximately 100p % of the (lambda, chi) pairs will
    fall between the plotted dashed horizontal control lines when X and Y are
    independently distributed (the null hypothesis).  The only allowed values
    of # are .90, .95, and .99 (or, equivalently, 90, 95, and 99).  The default
    is .95.

sample(%) allows a random subsample of the data to be selected for processing.
    The % given to sample() should be a value in the range: 0 < % < 100.  If
    hilite() is specified, the highlighted and non-highlighted subsets will be
    sampled separatedly to (approximately) yield the specified percentage of
    each subgroup.

    (Note that this option is offered because processing time for large samples
    is very long -- for example, exceeding 70 seconds on a 300MHz Pentium for a
    file of 8000 observations; this despite optimization of the code in version
    0.0.2 that reduced the time to one-third that of version 0.0.1.)

graph_options are those of Stata's twoway graph.  With the exception of
    saving(), options are applied equally to both the twoway scatterplot and
    the chiplot, so caution is warranted.

Examples

 . chiplot mpg weight                       (chi-plot of mpg against weight)
 . chiplot mpg weight if foreign            (same, but only foreign cars)
 . chiplot mpg weight, hilite(price<5000)   (same, but inexpensive cars
                                 highlighted)
 . chiplot mpg weight, hilite(foreign)      (same, but with foreign cars
                                 hilighted)
 . chiplot mpg weight, h(foreign) sam(50)   (same, but a 50% sample of each
                                 group)


Author

Thomas J. Steichen, RJRT, steicht@rjrt.com


Thanks to... 

Fred Wolfe for exercising the program and pointing out some useful enhancements
  now incorporated in this, version 0.0.2; and

Nick Cox and Bill Gould for discussions that led indirectly to notable