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Estimating Ability and Item-Selection Strategy in Self-Adapted Testing: A Latent Class ApproachAutonoma University of Madrid
This article presents a psychometric model for estimating ability and item-selection strategies in self-adapted testing. In contrast to computer adaptive testing, in self-adapted testing the examinees are allowed to select the difficulty of the items. The item-selection strategy is defined as the distribution of difficulty conditional on the responses given to previous items. The article shows that missing responses in self-adapted testing are missing at random and can be ignored in the estimation of ability. However, the item-selection strategy cannot always be ignored in such an estimation. An EM algorithm is presented to estimate an examinee’s ability and strategies, and a model fit is evaluated using Akaike’s information criterion. The article includes an application with real data to illustrate how the model can be used in practice for evaluating hypotheses, estimating ability, and identifying strategies. In the example, four strategies were identified and related to examinees’ ability. It was shown that individual examinees tended not to follow a consistent strategy throughout the test.
Key Words: EM algorithm • latent class modeling • missing at random • self-adapted testing
Journal of Educational and Behavioral Statistics, Vol. 29, No. 4,
379-396 (2004) 
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