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:Indeed, daily patterns of Epas1 mRNA is rhythmically expressed in the mouse heart with high levels at circadian time 8–12 (unpublished data), which precedes peak expression of mPai-1 mRNA (Minami et al., 2002; Oishi et al., 2005a).
Category: