Overlapping area represents the amount of risk that can be diversified away by holding EURONEXT BEL-20 and S&P 500 in the same portfolio assuming nothing else is changed. The correlation between historical prices or returns on SP 500 and EURONEXT BEL-20 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 EURONEXT BEL-20 are associated (or correlated) with SP 500. Values of the correlation coefficient range from -1 to +1, where. The correlation of zero (0) is possible when the price movement of SP 500 has no effect on the direction of EURONEXT BEL-20 i.e. EURONEXT BEL-20 and SP 500 go up and down completely randomly.