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:Indole-3-carbinol is used as standard reference compound as its chemopreventive potential by modulating the activities of phase I and phase II enzymes has been well established in the literature [20‚Äì24].
Category: