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:In the same way, the maximum E-CSF/E-serum ratio for RBP was detected at E4 but not at E3, coinciding with its suggested activity in retinol transport to the E-CSF (Parada et al., 2008).
Category: