Correlation calculates the Pearson product moment correlation coefficients for each pair of variables and it is used to test if variables are correlated. The correlation coefficient measures the magnitude of the linear relationship between two variables and it ranges from -1 and +1. If two variables are perfectly correlated such that when one variable increases, the other increases as well, the correlation coefficient is +1. On the other hand, if one variable increase while the other decreases, the correlation coefficient is negative.