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:Prevalence in brown rats ranged from 2 7% to 8 5% by culture (n = 3; number of animals: median = 256, range = 130–919) [82, 108, 117] but was considerably higher in three studies that used PCR to detect infection (10 0% to 4 7%; number of animals: median = 11, range = 10–96) [103, 118, 124].
Category: