Correlation only looks for linear relationships. For example, suppose we have a random variable X that takes values −2, −1, 1, or 2 each with probability 1⁄4. Define the random variable Y=X^2. The correlation is 0. Despite a functional relationship (causality if I’ve ever seen it), the two variables are uncorrelated.
Correlation only looks for linear relationships. For example, suppose we have a random variable X that takes values −2, −1, 1, or 2 each with probability 1⁄4. Define the random variable Y=X^2. The correlation is 0. Despite a functional relationship (causality if I’ve ever seen it), the two variables are uncorrelated.