Overlapping area represents the amount of risk that can be diversified away by holding Joy Global Inc and Ampco Pittsburgh Corp. in the same portfolio assuming nothing else is changed. The correlation between historical prices or returns on Ampco Pittsburgh and Joy Global 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 Joy Global are associated (or correlated) with Ampco Pittsburgh. Values of the correlation coefficient range from -1 to +1, where. The correlation of zero (0) is possible when the price movement of Ampco Pittsburgh has no effect on the direction of Joy Global i.e. Joy Global and Ampco Pittsburgh go up and down completely randomly.