AN ELEMENTARY TEST OF THE NORMAL 2PL MODEL AGAINST THE NORMAL 3PL ALTERNATIVE

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.