The 'Ability' Scale in Item Characteristic Curve Theory

Author(s):

Lord, Frederic M.

Publication Year:

1974

Report Number:

RB-74-19

Source:

ETS Research Bulletin

Document Type:

Report

Page Count:

21

Subject/Key Words:

National Science Foundation (NSF), Computer Software, Data Analysis, Item Response Theory, Mathematical Formulas, Models, Scaling, Test Theory

Abstract

For the six available sets of empirical data, the discrimination (slope) parameter alpha of the logistic item characteristic curve was found to have a significant positive correlation over items with the difficulty (location) parameter beta. This unpleasant situation can be eliminated by a suitably chosen transformation of the ability scale. An example of the transformation is given and some empirical results of using the transformed scale are shown. (21pp.)

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