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:This finding corresponds well with the results of Askaer et al. (2011); Couwenberg et al. (2011); Schäfer et al. (2012) and Audet et al. (2013b), who all reported negligible CH4 emissions when GWL was 20–30 cm below the soil surface, which is attributed to a restricted methane production zone and…
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