This Article Full Text (OnlineFirst PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Add to Saved Citations Download to citation manager Request Permissions Request Reprints Add to My Marked Citations Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Woods, C. M. Search for Related Content Social Bookmarking                   What's this?

Likelihood-Ratio DIF Testing: Effects of Nonnormality

^* To whom correspondence should be addressed. E-mail: cwoods{at}artsci.wustl.edu.

	Abstract

Differential item functioning (DIF) occurs when an item has different measurement properties for members of one group versus another. Likelihood-ratio (LR) tests for DIF based on item response theory (IRT) involve statistically comparing IRT models that vary with respect to their constraints. A simulation study evaluated how violation of the normality assumption about the random latent variable for one or both groups affected IRT-LR-DIF results. Item response data with or without DIF were generated from the two-parameter logistic model and fitted under the assumption that the latent distribution was normal for both groups. Although the IRT-LR-DIF method performed well when latent distributions were normal for both groups, results were distorted when the distribution was skewed for one or both groups. Specifically, Type I error was inflated, differences between reference- and focal-group item parameter estimates were inaccurate, and group differences in the mean and variance of the latent distribution were overestimated.

CiteULike    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?