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:The interaction between BBS4 and PCM-1 was first identified by a yeast two-hybrid screen using BBS4 cDNA as bait (20), and affinity purification confirmed that PCM-1 is associated with the stable BBS complex (12).
Category: