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:(33) showed that VT measured with whole body plethysmography was similar to that measured with pneumotachography under normal conditions in urethane-anesthetized mice, which suggests that the decompression component is small under such conditions.
Category: