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:Data evaluating the effect of resident level on postoperative outcomes are limited and conflicting and have not been previously assessed in a pediatric patient population.(9,13) The purpose of this study was to determine if the postgraduate level of the intraoperatively involved resident correlates with operative outcomes for pediatric patients undergoing laparoscopic appendectomy for appendicitis.
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