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help for vanelteren                                      Version 1.0 2004-05-09
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van Elteren's test (generalized Wilcoxon-Mann-Whitney ranksum test)

        vanelteren [depvar] [if exp] [in exp] [, by(groupvar) strata(varname)
                 ]


    by ...: may be used with vanelteren; see help by.



Description

    vanelteren performs van Elteren's generalization of the
    Wilcoxon-Mann-Whitney ranksum test, a modification that allows
    stratification or blocking on a variable.  It can be thought of as a
    nonparametric analogue of a randomized-blocks analysis of variance
    (ANOVA), that is, with a treatment factor (which may only have two
    levels) and a blocking or stratification variable that accounts for some
    heterogeneity in response.  depvar must be at least ordinal, and groupvar
    must be numeric.  The stratification (blocking) variable may be either
    string or numeric.  vanelteren calls ranksum for the within-stratum
    Wilcoxon statistics and weights them before combining them in an overall
    asymptotic test statistic.


Options

    by(groupvar) is not optional.  It specifies the name of the grouping
        variable.  This by() is separate from the by ...:  prefix and may be
        combined with the prefix.

    strata(varname) is likewise not optional.  It specifies the name of the
        stratification or blocking variable, which may be an independent
        unit, for example, a subject ID analogous to that specified by
        i(varname) in xtreg.



Remarks

    For more information on van Elteren's test, see E. L. Lehmann (and H. J.
    M. D'Abrera), Nonparametrics. Statistical Methods Based on Ranks (San
    Francisco:  Holden-Day, 1975), pp. 132-141.  This cites the original--P.
    H. van Elteren, On the combination of independent two-sample tests of
    Wilcoxon. Bulletin of the International Statistical Institute 37:351-61,
    1960.


Examples

    . vanelteren response, by(treatment) strata(clinic)

    . vanelteren likertscore, by(intervention) st(packsaday)


Author

    J. Coveney E-mail jcoveney@bigplanet.com if you observe any problems.


Also see

    Manual:  [R] signrank