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:Both this analysis and previous publications (Nühse et al., 2004; Hem et al., 2007) identified phosphorylation in vivo in the C-terminal region of PHT1;1 (Ser-514 and Ser-520) and PHT1;4 (Ser-524).
Category: