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 evaluation of the impact in the accuracy of the node’s response has been performed for each supported frequency by comparing the results with our reference model programmed in Matlab which mimics the node’s architecture and is already used in [3], [4], [5] and [6].
Category: