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