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 reasons for this disparity cannot be established from our data set, although in China, one barrier to effective provision of GOLD-recommended treatments has been identified as the self-administration of nonprescription medicines by individuals with COPD.(16) A particular focus of this study was translating the impact of increments in activity impairment on HCRU and work productivity.
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