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 use of a throat pack increased the risk of developing sore throat by more than 3 times; this finding is in contrast to previous studies in which the presence of a throat pack was not found to be a risk factor in the development of POST.17,18
Our patients predominantly underwent ENT surgery, in which it is common to use a throat pack to prevent blood from trickling into the stomach and leading to postoperative nausea and vomiting.
Category: