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:Hence, the ILD ABL response area analysis window included the physiologic ILD range ( 40 dB) characterized previously (Koka et al., 2008) and an ABL range from threshold to 40 dB above ABL threshold.
Category: