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:HRQOL was assessed with the Dutch language version of the EuroQol 5 Dimensions questionnaire (EQ-5D) using the summary score based on the tariffs by Dolan.22 The EQ-5D questionnaire is a multiattribute instrument reflecting the societal preferences and values for the five domains discerned and their mutual interdependence.
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