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:Using whole-Pg lysates, a Pg-specific lipopolysaccharide or recombinant citrullinated Pg PAD, other investigators have previously demonstrated increased frequencies of Pg antibody responses in patients with chronic RA compared with healthy control participants [5,13-16,22], as we did using whole-sonicate antigens.
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