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 coexistence of diagnostic indices of both normal and reduced systolic function is common and difficult to reconcile in HFpEF (Tan et al. 2009; Norman et al. 2011; Hiemstra et al. 2013; Marshall et al. 2013) and results from this study contribute to this interesting and often observed paradox.
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