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:…five experimental groups were selected to compare the metabolite profiles associated with different manifestations of IVA, as follows: (1) The first group consisted of children with the homozygous mutation of the IVD gene (homozygotes), but showing clinical variability (Dercksen et al. 2012).
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