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:The AoV and AAo were evaluated using a parasternal long-axis view, and the PV, MPA, LPA, RPA, and DA were evaluated using a parasternal short-axis view as per published guidelines [12].
Category: