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:Adult, 12‚Äì14 week-old male C57/Bl6 mice (n = 12/group) underwent constriction of the pulmonary artery or thoracic aorta as previously described to generate models of acute primary and progressive secondary RVPO respectively [14,19].
Category: