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:In addition, the discriminative power of the selection criteria used for a UK AS cohort (Selvadurai et al, 2013) and the effect of the number of biopsy cores (Ochiai et al, 2005) containing cancer were evaluated.
Category: