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:Furthermore, the hospital anxiety and depression scale (HAD) (Snaith and Zigmond, 1986) and the IBS special scale for quality of life (QOL) (IBSQOL) (Drossman et al., 2000) were used.
Category: