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:Preoperative radiographs were evaluated to determine the Paprosky score (18) and the American Academy of Orthopaedic Surgeons (AAOS) score (4) to classify the acetabular defects.
Category: