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:These results are in line with
 several other studies (Mattson 1980; Ayres and MacLean 1987; Kause et al. 1999; van der Wal et al. 2000; Graglia et al. 2001; Lempa et al. 2004; Hansen et al. 2006).
Category: