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:Thus, while the current study reproduces the spectral EEG changes induced by propofol in more detail than (Hutt and Longtin, 2010) which did not focus on reproducing spectral EEG peaks themselves, but instead on bi-phasic power changes, it is limited to the first phase of the bi-phasic response.
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