help mequate
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Title
    mequate -- Calculates equating constants A & B using Mean/Mean and
        Mean/Sigma Methods under the common-item non-equivalent groups design


Syntax
        mequate formx_a formx_b formx_cformy_a formy_b formy_c

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    Note: mequate currently equates forms with dichotomous items only.
      mequate also assumes that the 3PL models was used.


Description
    Calculates the equating constants A & B using the Mean/Mean and
    Mean/Sigma Methods under the common-item non-equivalent groups design
    (Kolen & Brennan, 2004). This procedure uses the item parameter estimates
    a, b, and c, from seperate calibrations of the 3PL model on each form (x
    and y). mequate then calculates the equating constants A and B that can
    be used to transform form x's scale onto that of form y. As arguments,
    mequate takes the item parameter estimates from the seperate calibrations
    of each form.  The item parameter estimates should be arranged in Stata
    such that each unique item occupies one row. Common items will then have
    item parameter estimates from the form x calibration and the form y
    calibration in the same row. Items that were only on one form will have
    item parameter estimates only in the columns pertaining to that form's
    calibration.



Options
    none no options are currently available.


Results
    Results are printed in the results window. The equating constants are
    also stored in the following scalars r(msa), r(msb), r(mma), and r(mmb).
    The number of common items is also printed.



Examples
. example
mequate xa xb xc ya yb yc

. example score transformation using results from the Mean/Sigma method.
gen testx_a_y=xa/`r(msa)'
gen testx_a_y=`r(msa)'*xb+`r(msb)'
gen testx_c_y=xc

Author
    L.W. McGuire, University of Minnesota-Twin Cities, Educational
    Psychology, contact: lwmcguir@umn.edu



References
    Kolen, M. & Brennan, R. (2004).  Test Equating, Scaling, and Linking.