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:Most of the various studies on axillary odor—its chemistry, gender differences, intensity, and related microorganisms— have been performed on Caucasians (Russell, 1976; Doty et al., 1978; Leyden et al., 1981; Rennie et al., 1991; Zeng et al., 1991, 1992, 1996a).
Category: