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:Level 1 patients require immediate lifesaving interventions, level 2 patients are in a high-risk situation, are lethargic, confused, or have severe pain, and levels 3, 4, and 5 patients need many, 1, or no resources, respectively.(19) All adult (ie, 18 years of age) nontrauma patients were eligible for inclusion to the study, if they had an ESI score of 2 or 3 and vital signs within the normal range and presented in 1 of the 2 EDs between May 24, 2007, and February 8, 2011.
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