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:were noted to influence pain perception in previous studies (Nafiu, Shanks, Abdo, Taylo, & Tremper, 2013; T√ºfekci et al., 2009) were obtained by a research assistant from the medical records.
Category: