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An Elementary Test of the Normal 2PL Model Against the Normal 3PL Alternative

Author(s):
Haberman, Shelby J.
Publication Year:
2006
Report Number:
RR-06-14
Source:
ETS Research Report
Document Type:
Report
Page Count:
8
Subject/Key Words:
2-Parameter Logistic (2PL) Model, 3PL Model, Praxis Series

Abstract

A simple score test of the normal two-parameter logistic (2PL) model is presented that examines the potential attraction of the normal three-parameter logistic (3PL) model for use with a particular item. Application is made to data from a test from the Praxis series. Results from this example raise the question whether the normal 3PL model should be used routinely in preference to the normal 2PL model unless evidence exists that a substantial gain in description of data is achieved.

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