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:, 2011); (ii) 99 metabolites allowed discrimination of humanised and gnotobiotic mice, although they possess quite distinct microbiota (85% of the microbial genera and species are different) (Marcobal et al., 2013); (iii) 43 metabolites were found to differ when comparing the human, mouse and rat faecal metabolomes (Saric et al.
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