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, a protein-binding glycoprotein (Termine et al., 1981; Kopp et al., 1992; Tiruppathi et al., 1996; Blazejewski et al., 1997), was investigated as a possible facilitator of albumin transfer across choroid plexus epithelial cells.
Category: