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Dominance diagram

domdiagvarname[ifexp] [inrange], by(byvar)[reversegraph_options]

Description

domdiagplots a dominance diagram given a division of the values of the numeric variablevarnameinto precisely two groups by the categories ofbyvar.Suppose there are

n_1values in the group for the lower value ofvarname(hereafter called group 1) andn_2values in the group for the higher value ofvarname(group 2). Then there aren_1*n_2pairwise comparisons, which are plotted on a graph with axes rank onvarnamewithin group 1 and rank onvarnamewithin 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 inranksum: the proportion of pairs symbolised"+"plus 1/2 the proportion of pairs symbolised"0"is the estimate thatP((varname| group 1) > (varname| group 2)).By default, ranks for the group with fewer values are plotted on the

yaxis.

RemarksThis 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.

domdiagtemporarily makes a dataset ofn_1*n_2observations. 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. Ifbyvardefines three or more categories and it is desired to focus on just two, make sure the others are excluded by usingif.

reversespecifies that axes are to be reversed from the default.

graph_optionsare options of scatter. By default,note()is used to displayP((varname| group 1) > (varname| group 2)).

Examples

. domdiag mpg, by(foreign)

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

ReferencesCliff, N. 1993. Dominance statistics: ordinal analyses to answer ordinal questions.

Psychological Bulletin114, 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 Review51, 25-38.Newson, R. 2002. Parameters behind "nonparametric" statistics: Kendall's tau, Somers' D and median differences.

Stata Journal2: 45-64. http://www.stata-journal.com/sjpdf.html?articlenum=st0007

Also seeManual:

[R] signrankOn-line: signrank