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:Previous empirical analyses of subnational consumer subsidies found that a majority of solar adoption was attributable to subsidies (e.g., Hughes and Podolefsky, 2015; Burr, 2016; De Groote and Verboven, 2016; Gillingham and Tsvetanov, 2017).
Category: