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ABSTRACT The basic equations of item response theory (IRT) provide a foundation for inferring examinees' abilities from responses to different test items. In practice, examinees do not generally provide a response to all items—for reasons that may or may not have been intended by the test administrator, and that may or may not be related to their ability. The mechanisms that produce missingness must be taken into account if correct inferences are to be drawn. Using concepts introduced by Rubin (1976), we discuss the implications for Bayesian and direct likelihood ability parameter estimation that are entailed by alternate test forms, targeted testing, adaptive testing, time limits, omitted responses, and examinee choice of tasks. Attention is focused on whether, in each case, the mechanism for missingness is “ignorable,” and, in those cases in which it is not, how it can be modeled.
Mislevy et al. (Sun,) studied this question.