Latent class analysis of differential item functioning on the peabody picture vocabulary test-III

This study investigated the use of latent class analysis for the detection of differences in item functioning on the Peabody Picture Vocabulary Test - Third Edition (PPVT-III). A two-class solution for a latent class model appeared to be defined in part by ability because Class 1 was lower in ability than Class 2 on both the PPVT-III and the Expressive Vocabulary Test (EVT). This difference was much larger on the PPVT-III for the low-ability class. No difference was found for the high-ability latent class, suggesting that the difference was a result of something in the PPVT-III that was not present in the EVT. The difference on the PPVT-III for low-ability children appeared to be a result of the structure of the items on the test, which seems to encourage the overriding use of the novel name - nameless category strategy for the selection of an answer - a strategy not available on the EVT.