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:Because TKA is a high-volume, high-cost medical intervention, it is not surprising health-related quality-of-life outcomes have been developed to allow investigators to quantify preoperative to postoperative improvements in TKA patient health status [7, 8, 11, 14, 16].
Category: