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:A number of clinical tools have been developed for the assessment of neuropathic pain, including the neuropathic pain questionnaire (NPQ) [2], ID Pain [3] and douleur neuropathique (DN4) [4] .
Category: