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:This is not surprising and may simply be due to the fact that unlike past studies, our sample comprised women who had already had an adult sexual assault at the start of the study, so their risk level was likely higher from the start, and the sample was more homogeneous than past studies of women in general (Livingston et al., 1997; Messman-Moore et al., 2010).
Category: