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:Using these additional analyses, some other authors observed no cleavage of a GFP fusion protein (Surribas et al. 2006, 2007; Tang et al. 2008; Sjöblom et al. 2012), indicating that the cleavage we observed is likely to be product-specific.
Category: