Manipulator is a free Excel Spreadsheet designed as an educational tool. It helps the IRT practitioners to see the changes in the Item Response Functions, Test Response Functions, Item Information Functions, Test Information Functions, Probability of a correct/incorrect response to the items and likelihood functions following the changes in the item parameters, examinee reponses and the Bayesian prior types. This is the third of the free IRT tool series from . I hope you and your students enjoy it.

Acknowledgment : I would like to thank Prof. David J. Weiss of the University of Minnesota for his invaluable suggestions to the first draft of this spreadsheet.

                                                                                                              Alper SAHIN, Ph.D.

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