The best replacement for covariance is correlation.

The best alternatives to covariance are rated as following:
★★★★★  correlation
★★★  variance
★★★  correlation coefficient
★★  standard deviation
★★  contravariance
★  coefficient of variation
★  correlation matrix
★  pearson correlation
  autocovariance
  contravariance c#
  correlation difference
  analysis of variance
  covariation
  correlations
  invariance

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Speaking about covariance, one probably shouldn't forget about correlation coefficient.

Other search terms related to covariance and their ratings are:
★★★★★ correlation coefficient
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covariance
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