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:Baumann et al (17) reported a single-center series of patients treated with the XTRACT procedure for ALI and showed similar results as the present study, with 78% efficacy (85.0% below the knee and 53.9% above the knee).
Category: