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 depth and length of MBs may be responsible for the severity of these conditions (Canyigit et al. 2009; Ferreira et al. 1991; Lazoura et al. 2010; Ozbag and Kervancioglu 2004; Santos et al. 2007).
Category: