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:Pain catastrophising was measured with the Pain Catastrophizing Scale (PCS) [26], a 13-item scale that measures the participant’s expression of worry and excessive focus on negative aspects of the painful situation, expectations of negative outcomes and the inability to cope effectively with pain [27].
Category: