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:These methods have been used in tremor research to study the relation between muscle activity (electromyogram (EMG)) and magnetoencephalogram (MEG) [Volkmann et al., 1996; Tass et al., 1998], between EMG and electroencephalogramm (EEG) [Jasper & Andrews, 1938; Schwab & Cobb, 1939; Hellwig et al.,…
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