The correlation coefficient is a descriptive measure of the strength of linear association between two variables, x and y. values of the correlation coefficient are always between -1 and +1. A value of +1 indicated that the two variables x and y are perfectly related in a positive linear sense. That is all data points are on a straight line that has a positive slope. A value of -1 indicates that x and y are perfectly related in a negative linear sense, with all data points on a straight line that has a negative slope. Values of the correlation coefficient close to zero indicates that x and y are not linearly related.