[http://www.statisticshowto.com/what-is-the-pearson-correlation-coefficient/]
Correlation between sets of data is a measure of how well they are related.
Correlation coefficients are used in statistics to measure how strong a relationship is between two variables. Pearson correlation is commonly used in linear regression.
原文：http://www.cnblogs.com/linxd/p/4900504.html