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:The proportion of long-chain poly-unsaturated FAs (in particular arachidonic acid, 20:4 n-6) and the average degree of FA unsaturation in skeletal muscle membrane PLs has been shown to correlate positively with insulin sensitivity (Borkman et al., 1993; Pan et al., 1995), whereas the proportion of 16:0 in both skeletal muscle PLs and TGs correlated negatively with insulin sensitivity (Vessby et al.
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