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Optimal Number of Strata for the Stratified Methods in Computerized Adaptive Testing

Published online by Cambridge University Press:  08 July 2014

Juan Ramón Barrada ,
Francisco José Abad  and
Julio Olea
Juan Ramón Barrada*
Affiliation:
Universidad de Zaragoza (Spain)
Francisco José Abad
Affiliation:
Universidad Autónoma de Madrid (Spain)
Julio Olea
Affiliation:
Universidad Autónoma de Madrid (Spain)
*
*Correspondence concerning this article should be addressed to Juan Ramón Barrada. Facultad de Ciencias Sociales y Humanas. Universidad de Zaragoza. 44003. Teruel (Spain). E-mail: barrada@unizar.es
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Abstract

Test security can be a major problem in computerized adaptive testing, as examinees can share information about the items they receive. Of the different item selection rules proposed to alleviate this risk, stratified methods are among those that have received most attention. In these methods, only low discriminative items can be presented at the beginning of the test and the mean information of the items increases as the test goes on. To do so, the item bank must be divided into several strata according to the information of the items. To date, there is no clear guidance about the optimal number of strata into which the item bank should be split. In this study, we will simulate conditions with different numbers of strata, from 1 (no stratification) to a number of strata equal to test length (maximum level of stratification) while manipulating the maximum exposure rate that no item should surpass (rmax) in its whole domain. In this way, we can plot the relation between test security and accuracy, making it possible to determine the number of strata that leads to better security while holding constant measurement accuracy. Our data indicates that the best option is to stratify into as many strata as possible.

Keywords

computerized adaptive testingitem exposure controltest securitystratified methods
Type
Research Article
Information
The Spanish Journal of Psychology , Volume 17 , 2014 , E48
Copyright
Copyright © Universidad Complutense de Madrid and Colegio Oficial de Psicólogos de Madrid 2014 

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