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:Our results on working memory performance are similar to those of earlier studies (e.g. Archbold et al., 2009; Cosentino et al., 2008; Naegele et al., 2006) in showing impaired working memory in the OSA group.
Category: