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:with PD (Blin et al. 1990; Hausdorff et al. 1998, 2001; Hausdorff 2005; Schaafsma et al. 2003; Springer et al. 2006; Yogev et al. 2005), leading one to speculate that a close association exists between gait variability and asymmetry.
Category: