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:Recent publications have revealed that the use of related types of e-crystallization growth cells applied to proteins by using direct current (DC) made crystals grow better oriented to the cathode (when the protein molecule was positively charged) compared to those crystals grown on the anode (when the protein molecule was negatively charged) showing also high crystal quality [16–20].
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