Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:In other words, the selectively bred animals would mainly differ in trait anxiety, which is an enduring feature of an individual and, consequently, does not vary from moment to moment, in contrast to state anxiety, which is provoked by an anxiogenic stimulus and only experienced at a particular moment in time (Belzung & Griebel, 2001; Lister, 1990).
Category: