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:…prevalence because of different definitions of depression, differences in depression screening methods, and different groups of participants (Massie & Holland, 1984; Ciaramella and Poli, 2001; Uchitomi et al., 2003; Katz et al., 2004; Ell et al., 2005; Boyd et al., 2012; Kim et al., 2012;…
Category: