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:…have shown that a depressive mood state and poor quality of life are less likely in elderly individuals who meet empirical minimum standards of habitual physical activity: >4,000 steps/day or >5 min/day at an intensity ≥3 metabolic equivalents (METs; Yasunaga et al., 2006; Yoshiuchi et al., 2006).
Category: