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 observed decrease of the CFF/FUF in our HE patients is well in line with the results of Kircheis et al. (2001a, 2001b, 2001c, 2002) and Timmermann et al. (2008).
Category: