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:[77] reported that the incidence of gastric adenocarcinomas in Wistar rats given MNNG (50llg/ml) for 25 weeks followed by a low protein diet (5% casein) was 63%, whereas those given a higher protein diet (10% and 25% casein) were 15% and 18%, respectively.
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