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 results from the present series are also broadly comparable to independent reports on the Oxford UKR, which have observed between 21% and 54% of revisions were performed for aseptic loosening (19,21,24), as well as those studies including a range of different UKR prostheses and reporting revision for aseptic loosening in 44% to 67% of cases (3,22).
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