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:…has been suggested that cognitive deterioration appears mainly at higher levels of depression and that inclusion of MS patients with mild depression leads to failure in detecting a relationship with cognitive impairment (Demaree, Gaudino, & DeLuca, 2003; Feinstein, 2006; Siegert & Abernethy, 2005).
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