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:Furthermore, similar to an early study by Thiriet and colleagues (10), Boiselle and colleagues have recently demonstrated that the highly collapsed trachea (>50% in cross-sectional area) on dynamicexpiratory CT scans, which is concordant with the current diagnostic criteria of TM/TBM, is frequently observed in subjects with normal lung function (9).
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