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:Similar results were obtained for several other plant species in previous studies (peanut, common bean, chestnut, black gram) (Raina et al. 2001; Marotti et al. 2007; Goulao et al. 2001, Souframanien and Gopalakrishna 2004).
Category: