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:Based upon this review of slides, cases were assembled into three case-series representing progressively more stringent de®nitions of OED, the most restrictive of which required that both blinded pathologists diagnose the case as having OED [8].
Category: