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:Such complex
mixtures are commonly investigated in metabolomics studies (Saric et al., 2008; Le Gall et al., 2011; Marcobal et al., 2013; Weir et al., 2013; Walker et al., 2014).
Category: