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:Antrochoanal polyps account for between 4 and 6 % of all nasal polyps, although they are much more frequently encountered in children, with an increased incidence of 35 % in the paediatric population [3].
Category: