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:It has previously been shown that members of the ADAM family of metalloproteinases are expressed in adult thymi [7,8,9,10,12,13] and that ADAM8 is expressed in fetal and adult thymi [12,13].
Category: