On Inaccuracies in Owen's Approximation for the Bayesian Ability Estimate.
CENTER FOR NAVAL ANALYSES ALEXANDRIA VA
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In computerized adaptive testing, an examinees ability is often estimated using Bayesian procedures. Its calculation is greatly simplified if one uses Owens approximation. However, when the test length is moderate e.g., 15 items, the accuracy of Owens approximation is inadequate for calculating the examinees score. This is illustrated using the nine power subtests in the Armed Services Vocational Aptitude Battery. The recommended procedure is to use Owens approximation for adaptive items selection, and to compute the exact Bayesian estimate after the entire test has been administered. Keywords Tablesdata.