Quantitative Methods Forum @ Norm Endler Room (BSB 164)
Speaker: Alyssa Counsell, York University
Department of Psychology
Title: Is Item-Level Non-Invariance Always Important?
Abstract: Differential Item Functioning (DIF) refers to measurement non-invariance across groups. In other words, DIF is present when individuals from two distinct groups with equivalent levels of the latent trait or ability demonstrate different response patterns. The implication is that group membership (instead of the latent trait) accounts for the difference in responding. There are several methods that test for DIF but I will use item response theory (IRT) in the current presentation. Specifically I will discuss DIF results that compare Canadian and German participants’ response patterns on each of the items of the General Self Efficacy Scale (Schwarzer & Jerusalem, 1995). The results demonstrate a practical concern for researchers. When DIF is present in some items, the implications for research are not always clear. In some instances the pattern of DIF may not consistently favour one group, and instead, item-level group differences may appear to cancel each other out if the total test information curve is examined. In psychology where groups are typically compared on test information rather than on an item-to-item basis, DIF may not represent a meaningful or important effect.