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:When X(D) ∼ N(μD, σ(2)), the two criteria will have the same optimum, that is, xJ = xC, but the variance of the non-parametric cut-point estimator optimizing the Youden index may be much larger than that of the concordance probability optimizer, Var ( x̂J ) > Var ( x̂C ) [6].
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