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Difficulty Index

When designing and developing educational and psychological tests, questionnaires, and assessments, measurement specialists attend directly to the qualities of the items making up the test or questionnaire. For example, it would be important to know whether an item is too easy or too difficult for the intended audience and uses of the test. Thus, estimating accurately an item’s difficulty index is important for good measurement and high-quality test design.

Estimating Item Difficulty

Contemporary test development practices rely on two broad statistical approaches for estimating item difficulty—classical test theory (CTT) and item response theory (IRT). The CTT approach draws on traditional statistical methods for estimating item difficulty. In the CTT framework, the proportion of examinees answering an item correctly or endorsing a particular response option on a questionnaire ...

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