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:SPARC has been proposed to be an albumin receptor in other epithelial tissues (Swaroop et al., 1988; Kopp et al., 1992; Tiruppathi et al., 1996), and is expressed at higher levels in human fetal tissue than in adult tissue and cell lines (Swaroop et al.
Category: