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:…power incision rule, however, demonstrates that the increase in erosivity that might accompany greater precipitation along the front would be accompanied by a reduction in channel gradient [e.g., Roe et al., 2002; Whipple et al., 1999], as the river is more effective at balancing rock uplift.
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