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 turn, quantification at the transcript level is also necessary to accurately estimate the expression of a given gene, which is merely the sum of all its isoforms (Jiang and Wong, 2009; Turro et al., 2011; Trapnell et al., 2013).
Category: