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:Five different pain rating scales with questionnaires included in the study were Wong-Baker Faces Pain Rating Scale (WBS) (2), Numerical Rating Scale (NRS) (3, 4), Faces Pain Scale- Revised (FPS-R) (2, 3, 5), Visual Analogue Scale (VAS) (2, 3, 4) and Verbal Rating Scale (VRS) (4).
Category: