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:As previously demonstrated by our group (20), the BHT model resembles human UIP because of clear evidence of alveolar collapse and chronic scarring, typically patchy subpleural or paraseptal distribution, evidence of active fibrosis as fibroblastic foci, and intervening normal areas.
Category: