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:The doses and volumes of the agonist and antagonist were the same as used in our previous studies (20, 21, 48, 52, 53, 55) and similar to those used by others (22, 35, 62, 68).
Category: