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:For power calculation in the linear regression analysis, we considered the magnitude of the gene-environment interaction, and according to Luan et al [50] an interaction was considered to be relevant in magnitude when the ratio of the two regression slopes [B1 for the genetic variable as additive in the first versus the second (B2) stratum was at least 2].
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