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:The Topic model (Griffiths et al., 2007; Steyvers & Griffiths, 2007) is based on the idea that context regions are collections of words that have been sampled from a mixture of latent topics.
Category: