Computing Pearson's Correlation Coefficient

The formula for Pearson's correlation takes on many forms. A commonly used formula is shown below. The formula looks a bit complicated, but taken step by step as shown in the numerical example, it is really quite simple.

Pearson formula

A simpler looking formula can be used if the numbers are converted into z scores:

where zx is the variable X converted into z scores and zy is the variable Y converted into z scores.

Computing Pearson's r in SPSS
Computing Pearson's r in EXCEL