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:Both the OS7 and OS8 lignin yields were approximately 65%, which was close to the lignin yields previously observed by Pan et al. (2006a) who employed higher temperatures and higher loadings of H2SO4 during the organosolv pretreatment.
Category: