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:Left ventricular ejection fraction (LVEF) was calculated using Teicholz‚Äôs M-mode formula while LV mass index (LVMI) was calculated using Devereux‚Äôs formula [10,11].
Category: