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:stemmed implants and augments) when revising a failed UKR is extremely variable and ranges from 11% to 76% in the literature and 33% in the present series (3,13,14,19,21,22,24).
Category: