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:…intrinsic activity for MOPr agonists (Traynor and Nahorski, 1995; Yu et al., 1997; Kovoor et al., 1998; Zaki et al., 2000; Clark et al., 2006; Saidak et al., 2006), however this parameter is not able to differentiate full agonists in terms of efficacy and can be highly dependent upon…
Category: