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:The meta-analysis was initially conducted on all the retrieved studies [9–22], and then separately on studies with a randomized [9, 10, 15, 18, 22] and observational [11–14, 16, 17, 19–21] design.
Category: