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:As described by Safran et al. (2005), these two latter basins differ geomorphologically from those of the central section because they have incised into the Altiplano and therefore skew the morphometric data (Zeilinger and Schlunegger 2007).
Category: