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:These results are more or less similar to study by (Nieschlag and Behre, 2001)which was 14.8% and 10.9% respectively and study of (Philippov et al, 1998) which was 10.9%, and lower than study by (Greenberg et al, 1978; Lipshultz and Howards, 1997) which was 37.4% and 42.2% respectively.
Category: