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:Following prior work (Haghighi et al., 2008; Prochasson and Fung, 2011; Vuliƒá and Moens, 2013b), we retain only nouns that occur at least 5 times in the corpus.
Category: