Covariance
If two variables are correlated (eg: house size and price), the main statistic used to measure this correlation between two variables is called covariance.
Covariance gives a sense of direction in which the two variables are moving:
- >0, the two variables move together.
- <0, the two variables move in the opposite direction
- =0, the two variables are independent
one problem with covariance is the values can be of completely different scales for each dataset (eg: 423,944,485 vs 0.0054) This makes it difficult to interpret such numbers.