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:Dogmatism, the tendency for individuals to be close-minded and driven by adherence to ideology in their beliefs, was measured using the 20-item version (Troldahl & Powell, 1965) of the Dogmatism Scale (DS; Rokeach, 1960; Rokeach & Fruchter, 1956).
Category: