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:Ozbag et al., found the prevalence of MBs to be 60 in 2002 (Ozbag et al. 2002) and 63 % in 2004 (Ozbag and Kervancioglu 2004) in sheep hearts.
Category: