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:TPC, TFC, FRAP, DPPH, and ORAC values were slightly different from, but comparable to, values in other reports (Cardador-Martinez et al., 2002; Heimler et al., 2005; Xu et al., 2007).
Category: