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 Hospital Anxiety and Depression Scale (HADS) is a self-completed 14-item screening questionnaire on a 4-point scale (Snaith and Zigmond, 1986), and was used to grade the severity of neuropsychiatric symptoms.
Category: