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:It is small (38 mm637 mm618 mm ), lightweight (925 g) and has been demonstrated to measure physical activity in children reliably when compared with heart rate monitoring [16] indirect [9] and room [4] calorimetry, and doubly labelled water [17] techniques.
Category: