“…The purpose of this paper is not to address the issue of identifiability for any of the models above in much detail, nor is it to derive sufficient restrictions to identify these models. Discussions of those topics may be found, for instance, in , Verhelst (2002), Fischer (2004), , ), Reiersøl (1950, ), San Martín, Gonzáles, and Tuerlinckx (2009), San Martín, Jara, Rolin, and Mouchart (2011, and . However, as parameter linking, which is the focus of this paper, is required due to lack of identifiability, we present some concepts related to identifiability and then present a few examples that demonstrate the lack of identifiability of polytomous IRT models.…”