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:We gave participants the
opportunity to write messages in support of American troops combatting ISIS: we assigned a score of 100 to participants who chose to write a message, and a score of 0 to those who did not (Kteily et al., 2015, Study 5).
Category: