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