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:However, it has to be noted that our study did not investigate other important disturbance aspects such as the interactive effects of disturbance frequency and spatial extent, which can influence competitive outcomes and thus species diversity (Miller et al. 2012a).
Category: