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:We used a global database of 1054 river basins across the world (Brosse et al. 2013) for which the native and nonnative status in each basin has been recorded for 9722 freshwater fish species.
Category: