correlation

noun3

1. •
   A reciprocal, parallel or complementary relationship between two or more comparable objects.
2. •
   One of the several measures of the linear statistical relationship between two random variables, indicating both the strength and direction of the relationship.

   • For example, scientists can use data from larger studies about the correlation between antibody levels and vaccine efficacy in adults to make a prediction about vaccine efficacy in children. — 2022
3. •
   An isomorphism from a projective space to the dual of a projective space, often to the dual of itself.