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:To compare acute reduction of hERG surface protein to a well-characterized inhibitor of hERG forward trafficking, pentamidine, a chemiluminescence assay was used (Kuryshev et al. 2005; Wible et al. 2005).
Category: