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:dN and dS were calculated for the aligned regions using the codeml programme from the PAML package [56], with default settings for pairwise analyses and nine free parameters used to account for codon frequencies (F3X4; [57]).
Category: