On Inaccuracies in Owen's Approximation for the Bayesian Ability Estimate
Published Date: February 1, 1986
In computerized adaptive testing, an examinee's ability is often estimated using Bayesian procedures. Its calculation is greatly simplified if one uses Owen's approximation. However, when the test length is moderate (e.g., 15 items), the accuracy of Owen's approximation is inadequate for calculating the examinee's score. This is illustrated using the nine power subtests in the Armed Services Vocational Aptitude Battery. The recommended procedure is to use Owen's approximation for adaptive item selection, and to compute the exact Bayesian estimate after the entire test has been administered.
