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:, 2009), it has been infrequently used in alcohol research (Johnson & Robinson, 2008), despite some notable exceptions (Krentzman et al., 2013; Robinson et al., 2007; 2011).
Category: