------------------------------------------------------------------------------- help forchiplotexperimental version 0.0.2, a Stata v7 program -------------------------------------------------------------------------------

Chi-plot: Nonparametric Graphical Assessment of Dependence

chiplotyvarname xvarname[ifexp] [inrange] [,hilite(exp)ci(#)sample(%)graph_options]

Description

chiplotis 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 AmericanStatistician55(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(#)setsp=#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 tosample()should be a value in the range: 0 <%< 100. Ifhilite()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_optionsare those of Stata's twoway graph. With the exception ofsaving(), 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)

AuthorThomas 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