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:Physical functioning was assessed with the Short Physical Performance Battery (SPPB) comprising balance tests with the aim to be able to maintain standing balance for ten seconds in three different positions, a timed four meter walk and a timed chair stand test [17].
Category: