A caveat, though, in quantum field theory, we sometimes have nonpositive states and in that case, a probabilistic interpretation makes no sense. At any rate, even in ordinary quantum field theory, we need to work with quantum probability instead of classical probability.

- Correlation
- Spearman's rank correlation coefficient
- Pearson product-moment correlation coefficient
- Correlation function (astronomy)
- Correlation function (statistical mechanics)
- Correlation function (quantum field theory)
- Mutual information