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help for domdiag
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Dominance diagram

domdiag varname [if exp] [in range] , by(byvar) [ reverse
graph_options ]

Description

domdiag plots a dominance diagram given a division of the values of the
numeric variable varname into precisely two groups by the categories of
byvar.

Suppose there are n_1 values in the group for the lower value of varname
(hereafter called group 1) and n_2 values in the group for the higher
value of varname (group 2). Then there are n_1 * n_2 pairwise
comparisons, which are plotted on a graph with axes rank on varname
within group 1 and rank on varname within group 2. The symbols used are
"+" if value in group 1 > value in group 2, "0" if value in group 1 =
value in group 2, and "-" if value in group 1 < value in group 2. This
helps to make graphic what is done in ranksum: the proportion of pairs
symbolised "+" plus 1/2 the proportion of pairs symbolised "0" is the
estimate that P((varname | group 1) > (varname | group 2)).

By default, ranks for the group with fewer values are plotted on the y
axis.

Remarks

This graph was used by Cliff (1993, 1996). Some earlier related ideas are
reviewed by Fisher (1983). Newson (2002) gives a broader discussion and
an example implementing domdiag.

domdiag temporarily makes a dataset of n_1 * n_2 observations.  This may
be very much larger than the existing dataset and the user should make
sure that enough memory is allocated.

Options

by(byvar) specifies subdivision into two groups and is a required option.
If byvar defines three or more categories and it is desired to focus
on just two, make sure the others are excluded by using if.

reverse specifies that axes are to be reversed from the default.

graph_options are options of scatter.  By default, note() is used to
display P((varname | group 1) > (varname | group 2)).

Examples

. domdiag mpg, by(foreign)

Author

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

References

Cliff, N. 1993. Dominance statistics: ordinal analyses to answer ordinal
questions. Psychological Bulletin 114, 494-509.

Cliff, N. 1996. Ordinal methods for behavioral data analysis.  Mahwah,
NJ: Lawrence Erlbaum.

Fisher, N.I. 1983. Graphical methods in nonparametric statistics:  a
review and annotated bibliography. International Statistical Review
51, 25-38.

Newson, R. 2002. Parameters behind "nonparametric" statistics:  Kendall's
tau, Somers' D and median differences.  Stata Journal 2: 45-64.
http://www.stata-journal.com/sjpdf.html?articlenum=st0007

Also see

Manual:  [R] signrank
On-line:  signrank

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