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:[25] compared the accuracy of the assessment of EF, EDV and ESV by eight-slice CT-gated SPECT and 2-D echo to the reference method cine MR and observed better correlation between gated CT and MR than between 2-D echo or gated SPECT and MR.
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