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:…isoforms, despite the use of different experimental endpoints such as production of inositol phosphates (Brauner-Osborne
and Krogsgaard-Larsen 1999), competitive binding (Green et al. 2000; Kaupmann et al.
1998a; Malitschek et al. 1998) or coupling to Kir3 channels (Kaupmann et al. 1998a).
Category: