Pearson product-moment correlation coefficient
The Pearson product-moment correlation coefficient describes how well a set of points follows a line in a graph. The coefficient is always a number somewehere from -1 to 1. The more line-like the points behave in their totality, the closer the value is to -1 or to 1. If it is near 0 or equal zero, there is little or no linearity to be detected.