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:Rodent and avian NF-M subunits, while otherwise very similar to their human counterpart, contain only one or two degenerate KSPV repeats (Levy et al., 1987; Napolitano et al., 1987; Zopf et al., 1987).
Category: