A quadratic curve test equating method for equating
different test forms under a random-groups data collection
design is proposed. This new method extends the
linear equating method by adding a quadratic term to
the linear function and equating the first three central
moments (mean, standard deviation, and skewness) of
the test forms. Procedures for implementing the
method and related issues are described and discussed.
The quadratic curve method was evaluated using real
test data and simulated data in terms of model fit and
equating error, and was compared to linear equating,
and unsmoothed and smoothed equipercentile equating.
It was found that the quadratic curve method fit
most of the real test data examined and that when the
model fit the population, this method could perform at
least as well as, or often even better than, the other
equating methods studied. Index terms: equating,
equipercentile equating, linear equating, model-based
equating, quadratic curve equating, random-groups
equating design, smoothing procedures.
Wang, Tianyou & Kolen, Michael J. (1996). A quadratic curve equating method to equate the first three moments in equipercentile equating. Applied Psychological Measurement, 20, 27-43. doi:10.1177/014662169602000103
Wang, Tianyou; Kolen, Michael J..
A quadratic curve equating method to equate the first three moments in equipercentile equating.
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