Measures of correlation and mixtures of product measures
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Total correlation (`TC') and dual total correlation (`DTC') are two classical measures of correlation for an n-tuple of random variables. They both reduce to mutual information when n=2. The first part of this paper sets up the theory of TC and DTC for general random variables, not necessarily finite-valued. This generality has not been exposed in the literature before. The second part considers the structural implications when a joint distribution μ has small TC or DTC. If TC(μ) = o(n), then μ is close in the transportation metric to a product measure: this follows quickly from Marton's classical transportation-entropy inequality. On the other hand, if DTC(μ) = o(n), then the structural consequence is more complicated: μ is close to a mixture of a controlled number of terms, most of them close to product measures in the transportation metric. This is the main new result of the paper.
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