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:Syllables with a voiced onset developed a low tone, and those with a voiceless initial induced a high tone, resulting in a six-way tonal contrast (2 pitch heights x 3 contours).1
(Kang 2014, Kim 2000, Oh 2011, Silva 2006, Wright 2007).
Category: