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:In (Premebida et al 2015), and in accordance with the experiments carried out in (Ullah et al 2008), exhaustive experimental results were reported for different conditions of illumination and portions (“A” and “B”), and separately for STD and EXT sequences.
Category: