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:, reads originating from constitutive exons) or even to unique genomic locations, transcript- and gene-expression levels can only be estimated with some degree of certainty, that is, with estimation error (Jiang and Wong, 2009; Turro et al., 2011; Trapnell et al., 2013).
Category: