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:This validation can be readily done using a specific PCR and PCR product sequencing, for which miR-RACE can be prefered method due to its effectiveness in the validation of precise sequences, especially both ends of miRNAs [19,36].
Category: