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:East Asian H. pylori strains possess a D motif within CagA in place of the western C motif and this has been shown to be a potent inducer of SHP-2 phosphatase (Higashi et al., 2002a; Azuma et al., 2004).
Category: