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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.

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