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:These findings are in accordance with those of other authors reporting postoperative improvement of VF in 75–92% and no improvement or worsening of VF in 8–19% of the patients [2, 4, 7, 15, 17, 21].
Category: