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:The level of the participants’ dementia varied from mild to extremely severe, as assessed by Mini Mental State Examination (MMSE) [20], Clinical Dementia Rating (CDR) [21] or Global Deterioration Scale (GDS) [22].
Category: