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:So far, various investigations on the chemistry and microbiology related to the axillary odor have been performed, most of them on Caucasians (Russell, 1976; Doty et al., 1978; Leyden et al., 1981; Rennie et al., 1991; Zeng et al., 1991, 1992, 1996a).
Category: