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