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:the total number of pedestrians leaving each tram that met the observation criteria, regardless of their ascent method, was entered as a continuous variable (mean=78 pedestrians per tram, range 21–156) [11, 12].
Category: