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Equating an Adaptive Test to a Linear Test (CT0401) by Wim J. van der Linden, University of Twente, Enschede, The Netherlands Executive Summary A popular method of reporting scores on a computerized adaptive test (CAT) is to convert each test taker’s CAT score to a numbercorrect score on a linear reference test; for example, a previous paperandpencil form or a special form assembled to the same content specifications as the CAT. This conversion is accomplished through a statistical process called test equating. Traditionally, two methods are used to carry out the equating that this score reporting method requires: (1) the equipercentile equating method, which determines the equated score by matching the percentiles for the CAT scores to those for the numbercorrect scores on the reference test, and (2) the test characteristic curve transformation equating method, which applies item response theory (IRT) to determine the reference test score that would correspond to each test taker’s CAT score. (Note that IRT is a mathematical model that is commonly used to analyze test data.) 