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:…skeletal muscle lipid esters have been shown to be related to variations in insulin sensitivity (16:0, 16:1, 18:2 n-6, 20:3 n-6, 20:4 n-6 and SFA) (Salomaa et al., 1990; Borkman et al., 1993; Vessby et al., 1994, 2002; Pan et al., 1995; Lovejoy et al., 2001; Pelikanova et al., 2001; Vessby, 2003).
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