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:The mutation rates we measured in pandemic V. parahaemolyticus were similar to those observed in E. coli O157:H7 and Y. pestis by PSPE; values observed were from 3.461026 to
4.061024 for E. coli and 8.561026 to 3.761024 for Y. pestis [31,32].
Category: