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:It was demonstrated previously that BPD provides excellent results in long-term weight loss maintenance, resolution or improvement of severe metabolic disorders that are often associated with obesity, and ultimately improved QOL.(7-12,16-22,33-36) Conversely, restrictive procedures have not provided the same satisfactory results in other reports, particularly in controlling type 2 diabetes.
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