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:IL-13 concentration was chosen based on previous publications in human airway epithelial cell cultures[10,21-23], and measurement of IL13 protein in bronchoalveolar lavage fluid of asthmatics with a segmental allergen challenge[24].
Category: