Overlapping area represents the amount of risk that can be diversified away by holding National American University H and Ryder System Inc in the same portfolio assuming nothing else is changed. The correlation between historical prices or returns on Ryder System and National American is a relative statistical measure of the degree to which these equity instruments tend to move together. The correlation coefficient measures the extent to which returns on National American University Holdings are associated (or correlated) with Ryder System. Values of the correlation coefficient range from -1 to +1, where. The correlation of zero (0) is possible when the price movement of Ryder System has no effect on the direction of National American i.e. National American and Ryder System go up and down completely randomly.