In statistics, Pearson product moment correlation coefficient (English: PPMCC or PCCs or PMCC, often expressed as R or Pearson 'sr Sr in this paper) is used to measure the correlation (linear correlation) between two variables X and Y, and its values are between-1 and 1. In natural science, this coefficient is widely used to measure the degree of correlation between two variables. It evolved from Francis Galton's similar but slightly different idea of 19 put forward by karl pearson in 1980s. This correlation coefficient is also called Pearson correlation coefficient R.