There are several formulas that can be used to
compute Pearson's correlation. Some formulas make more conceptual
sense whereas others are easier to actually compute. We are
going to begin with a formula that makes more conceptual sense.

To compute the correlation between
the variables X and Y, begin by computing
the mean for X and subtracting this mean from all values of
X. The new variable is called "x." The variable "y"
is computed similarly. The correlation is then computed using
the following formula:

An alternative computational formula that avoids
the step of computing deviation sores is: