Equipercentile equating of the Basic Ability and Knowledge Test (EXHCOBA)

Abstract

Equipercentile equating method is a statistical procedure where student raw scores of two different versions of the same test are considered equated if they correspond to the same percentile range. A graphic curve is presented to describe the difficult differences from version to version of a test. This work was aimed to estimate the equipercentil equating values, by academic content area, of the Basic Ability and Knowledge Test (EXHCOBA, by its Spanish acronym) that is used by the University of Baja California (UABC) as a selection student test. This norm-referenced test has excellent quality standards, a high technological development, several reliability and validity support studies, and others good psychometric parameters. Estimation of equating parameters was done applying the analytic method described by Kolen and Brennan (1995), with the random group procedure utilized by UABC to collect data. Results shows that equating was effective to adjust four statistical moments (mean, standard deviation, bias, and kurtosis) of the frequency distributions of EXHCOBA´s version 3 and 4 compared with version 2, by content area, producing equal score distributions. Nevertheless, irregularities appeared at the ends of the curves that suggests the need of a smoothing procedure.