Pearson coefficient

Pearson correlation coefficient is the test statistics that measure the statistical relationship, or association, between two continuous variables. It is known as the best method of measuring the association between variables of interest because it is based on the method of covariance. It gives information about the magnitude of the association, or correlation, as well as the direction of the relationship. The Pearson correlation coefficient is a measure of the strength of the linear relationship between two variables.

where Oi is the observation value and Pi is the forecast value and Obar is average of observation values and Pbar is average of forecast values.