The Coefficient of Correlation is used to express the strength of the relationship between two variables.
The coefficient of correlation has a value between -1 and +1. A coefficient of +1 means perfect positive correlation. A coefficient of -1 means perfect negative correlation (when one variable increases the other decreases). A coefficient close to zero means the variables are not related. Correlation is used in Regression Analysis.
The coefficient of correlation is conventionally called 'R'. Examples of values of R are:
The formula for R is: