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:…and selection of studies
We used a database of 1344 articles on the psychological treatment of depression that has been described in detail elsewhere (Cuijpers et al. 2008b, 2011), and that has been used in a series of earlier published meta-analyses (www.evidencebasedpsychotherapies. org).
Category: