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:This study provided further evidence that VTC is a sensitive measure of instability that may act as a control variable in
the regulation of upright standing posture (Slobounov et al. 1998; Van Wegen et al. 2001, 2002; Haibach et al. 2007).
Category: