Abstract
Objective
To demonstrate the value of item response theory (IRT) and differential item functioning
(DIF) methods in examining a health-related quality-of-life measure in children and
adolescents.
Study Design and Setting
This illustration uses data from 5,429 children using the four subscales of the PedsQL™
4.0 Generic Core Scales. The IRT model-based likelihood ratio test was used to detect
and evaluate DIF between healthy children and children with a chronic condition.
Results
DIF was detected for a majority of items but canceled out at the total test score
level due to opposing directions of DIF. Post hoc analysis indicated that this pattern
of results may be due to multidimensionality. We discuss issues in detecting and handling
DIF.
Conclusion
This article describes how to perform DIF analyses in validating a questionnaire to
ensure that scores have equivalent meaning across subgroups. It offers insight into
ways information gained through the analysis can be used to evaluate an existing scale.
Keywords
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Article info
Publication history
Published online: September 14, 2007
Accepted:
May 12,
2007
Identification
Copyright
© 2008 Elsevier Inc. Published by Elsevier Inc. All rights reserved.
