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:6756 [age, years]; Roza & Shizgal, 1984), multiplying resting energy expenditure by an activity factor to estimate nonexercise activity thermogenesis (Food and Agriculture Organization of the United Nations, World Health Organization, & United Nations University, 2001; Livingstone et al., 1991; National Academy of Sciences, 2005), and adding an estimate of average daily exercise energy expenditure calculated using activity-specific metabolic equivalents from the American College of Sports Medicine Compendium of Physical Activity (Ainsworth et al.
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