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 would also be consistent we our earlier study showing a threshold effect in electric field sensitivity, as evidenced by a sigmoidal dose–response curve (Kindzelskii and Petty 2000), which is a widelyrecognized feature of systems exhibiting cooperativity.
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