Cov (X,Y) = E [XY] - E [X] E[Y] ,or
Cov (X,Y) = E [XY] - x y
Ex.13 Find the covariance between X and Y in Example 1. (X = number of defective welds)
= 0.064 - (0.12) (0.148) = 0.046
Cov (X,Y) = E [XY] - E [X] E [Y]
= 1710 - 9.5 (180) = 0 Correlation While covariance measures the direction of the association between 2 random variables, the correlation measures the strength of the association.
Def. The correlation coefficient of X and Y,
= 