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:Only the statistically powered NLST study, with a sample size of 53,454, has detected a 20% mortality reduction with low-dose CT screening over chest X-ray screening [5], which was why we simulated 100,000 participants to obtain robust results.
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