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help for wridit                                                  (Roger Newson)
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Generate weighted ridits

        wridit varname [if] [in] [weight] , generate(newvarname)
                     [ by(varlist) folded reverse percent float ]

    fweights, pweights, aweights, and iweights are allowed; see weight.


Description

    wridit inputs a variable and generates its weighted ridits.  If no
    weights are provided, then all weights are assumed equal to 1, so
    unweighted ridits are generated.  Zero weights are allowed, and imply
    that the ridits calculated for the observations with zero weights will
    refer to the distribution of weights in the observations with nonzero
    weights.


Options

    generate(newvarname) must be specified.  It specifies the name of the
        generated output variable, containing the weighted ridits.

    by(varlist) specifies a list of by-variables.  If by() is specified, then
        the weighted ridits are computed within by-groups.

    folded specifies that the weighted ridits generated will be folded
        ridits.  A folded ridit, on a proportion scale from -1 to 1, is
        defined as 2*R-1, where R is the corresponding unfolded ridit (on a
        proportion scale from 0 to 1).

    reverse specifies that the weighted ridits will be reverse ridits, based
        on reverse cumulative probabilities.

    percent specifies that the weighted ridits will be generated on a
        percentage scale from 0 to 100, or from -100 to 100 if folded is
        specified.  If percent is not specified, then the weighted ridits
        will be generated on a proportion scale from 0 to 1, or from -1 to 1
        if folded is specified.

    float specifies that the weighted ridits will be generated with storage
        type float.  If float is not specified, then the weighted ridits will
        be generated with storage type double.


Remarks

    Ridits were introduced by Bross (1958).  Given a variable X, the unfolded
    ridit for a value x is equal to the probability that X<x plus half the
    probability that X==x.  The folded ridit for x is equal to the
    probability that X<x minus the probability that X>x.  Nicholas J. Cox
    introduced an egen function ridit(), computing unweighted ridits, as part
    of the egenmore package, downloadable from SSC.


Examples

        . wridit mpg, gene(wrid1)

        . wridit mpg [pwei=weight], gene(wrid2) by(foreign)


References

    Bross, I. D. J.  1958.  How to use ridit analysis.  Biometrics 14(1):
        18-38.


Author

    Roger Newson, National Heart and Lung Institute, Imperial College London,
    UK.
    Email: r.newson@imperial.ac.uk


Also see

     Manual: [D] egen
    On-line: help for egen
             help for egenmore if installed