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 2004 and 2005, we analysed variation in the concentration of carotenoids in relation to embryo sex in a nondestructive way (see Rubolini et al., 2006b; Saino et al., 2008a).
Category: