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:Based on available direct experimental measurements on several apparent two-state proteins [32, 33], here the intrinsic enthalpic folding barrier H ‡ i is taken, as a first approximation, to be a constant (independent of Gf/T ) for a given protein, but may differ for different proteins [29, 31].
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