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:In the experiments reported here, we used SFOLD [30] to estimate the marginal distribution at each nucleotide over structural contexts (e.g. paired, unpaired, hairpin loop) for each position of the sequence by sampling a large number of structures for the sequence according to the Boltzmann distribution.
Category: