Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

Date of Graduation

Spring 5-6-2011

Document Type


Degree Name

Doctor of Philosophy (PhD)


Department of Graduate Psychology


Christine E. DeMars

Robin Anderson

Joshua Goodman


In order to be able to fairly compare scores derived from different forms of the same test within the Item Response Theory framework, all individual item parameters must be on the same scale. A new approach, the RPA method, which is based on transformations of predicted score distributions was evaluated here and was shown to produce results comparable to the widely used Stocking-Lord (SL) method under varying conditions of test length, number of common items, and differing ability distributions in a simulation study. The new method was also examined using actual student data and a resampling analysis. Both the simulation study and actual student data study resulted in very similar transformation constants for the RPA and SL methods when 15 or 10 common items were used. However, the RPA method produced greater variance, especially when only 5 common items were used in the actual student data analysis compared to the SL method. The simulated and actual data research findings demonstrate that the RPA method is a viable option for producing the transformation constants necessary for transforming separately calibrated item parameter estimates prior to equating.

Included in

Psychology Commons



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