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:Data analysis: Primers for SSU rDNA genes are from Medlin et al. (1988) with three additional primers used to generate overlapping sequences from each clone as described in Snoeyenbos-West et al. (2002).
Category: