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:Background It is estimated that, at the time of diagnosis of type 2 diabetes mellitus, more than 10 % of patients have one or two risk factors for foot disease, such as peripheral neuropathy (PN) or peripheral vascular disease (PVD) [1].
Category: