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 difference in results in comparison with those of Becker and Chaushu (2000) may be due to the limitation of including only patients with unerupted canines and omitting those with ectopic eruption of these teeth in the present study.
Category: