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 explanation is consistent with the observation that Swiss mice were unable to respond to surgical removal of some of their mammary tissue by elevation of milk production in the remaining tissue (Hammond et al., 1996) which is also consistent with the peripheral limitation hypothesis.
Category: