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:Our results indicated that concentrations of CRP, Hp and SAA increased significantly in pigs infected with H1N2, but these increases were smaller than reported previously for various bacterial pig diseases (Heegaard et al., 1998; Sorensen et al., 2006; Pomorska-Mól et al., 2011a, b).
Category: