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:We evaluated 22 prospective cohorts in which HHV-8 DNA quantification had been performed on oropharyngeal swabs, including 18 cohorts from the Virology Research Clinic, University of Washington [14, 28–32], and 4 studies by affiliated investigators in Lima, Peru [33]; Kampala, Uganda [4]; Mombasa, Kenya [34]; and Yaounde, Cameroon.
Category: