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 our study, we found that mRNA and protein expressions of ER stress markers (p-eIF2α, ATF4, CHOP, p-IRE1, and sXBP1) [13–15] in
Category: