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help for backrasch
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Backward procedure on a Rasch model

        backrasch varlist , [method(keyword) test(keyword) nodetail p(#.###)
              nbscales(#) noautogroup]

Description

    backward realizes a Backward procedure on a Rasch model: the items are
        removed one per one if they have a bad fit to the Rasch model. The
        fit of the items is valuated by a first-order statistics (test R1c,
        R1m or Q1) It is possible to build several sub-scales of items, the
        second sub-scale is build with the items unselected in the first
        sub-scales, the third one with the items unselected in the two first
        sub-scales, and so on... By default, the parameters of the Rasch
        model are estimated by conditional maximum likelihood (CML), but it
        is possible to estimate them by marginal maximum likelihood (MML) or
        generalized estimating equations (GEE).

Options

    method(cml/mml/gee) defines the method of estimation of the difficulty
        parameters among conditional maximum likelihood (cml - by default),
        marginal maximum likelihood (mml) or generalized estimating equations
        (gee).

    test(R/Q) defines the first order statistics to use between R-type test
        (R1c or R1m - by default) or the Q1 test of Van den Wollenberg.

    nodetail does not display the description of the algorithm.

    p(#.###) defines the level of signification who define a significantly
        bad fitted item (0.05 by default).

    nbscales(#) defines the maximal number of sub-scales to build. By
        default, the program builds only one sub-scale.

    noautograoup forces the program to compute the first order fit statistics
        with the groups defined by the value of the score. by default, the
        scores are grouped to obtained groups of 30 individuals or more.

Examples

    . backrasch item1 item2 item3 item4 /*estimation by CML, test R1c, only
        one scale is built*/

    . backrasch item1 item2 item3 item4 , p(0.2) method(mml) nodetail
        /*estimation by MML, test R1m, only one scale*/

    . backrasch item1 item2 item3 item4 , p(0.1) nbsc(5) noautog /*CLM
        estimation, R1c tests, 5 scales will be build*/

Author

    Jean-Benoit Hardouin, Regional Health Observatory (ORS) - 1, rue Porte
        Madeleine - BP 2439 - 45032 Orleans Cedex 1 - France. You can contact
        the author at jean-benoit.hardouin@orscentre.org and visit the