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:Sessions were conducted at the same time of day for each participant after a 4-hr postprandial period during which no food was consumed, in accordance with previous studies including that of Carter et al. (2004). Participants were instructed to abstain from alcohol, caffeine, tobacco, and exercise during the 24-hr period before each visit.
Category: