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 reported normal range for GFAP (95% of all healthy subjects) is\0.3 ng/ml
(Missler et al. 1999) and for NSE B 13 ng/ml (Bremnes et al. 2003).
Category: